tl;dr: Sims with Adult ratings but General liberties (= no nudity) aren't always run by older, conservative, uptight Americans who hate kids. They're often run by people who aren't native English speakers, who don't know that "Adult" has a meaning beyond "grown-up" and whose culture completely demonises nudity.

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I've come to the realisation that there's another factor in why ratings can't be trusted, neither in general (when Adult sims have the same liberties that General sims can have) nor on OSW (when the OSW rating is different from the in-world rating): We're from different countries with different cultures and different languages.

This clashes with the culture of Second Life which supposes that everyone is an American or even from Northern California. OpenSim is still forced to hold on to this because neither Ubit nor the viewer teams have the development capacities to deviate from it.

An American will know by heart right off the bat what "General", "Moderate" and "Adult" may mean. The official definitions are more or less only there to specify the meanings. But it may be somewhat less clear for a Brit, a Canadian, an Australian etc. unless they've fully picked up American culture. It doesn't help that most grids by far don't have their definitions of the ratings written down anywhere. Why write down what "everybody knows"?

It's even worse for people from non-English-speaking countries. This may come as a surprise, but not exactly few of them can only use OSW by running the entire website through Google Translate. But when Google Translate translates "General", "Moderate" and "Adult", it neither necessarily gives out the same translations as in the viewer, nor does it necessarily give out a translation with the same associations as Americans have with "General", "Moderate" and "Adult".

For one, this is why particularly sims run by people with a different native tongue than English tend to rate their sims differently in-world and on OSW. On OSW, they have Googlish for "General", "Moderate" and "Adult"; in their viewer, they have more sensible translations by people who actually know that language. And they may fail to see a parallel between these. Not knowing what to choose, they end up just clicking on something because they have to.

I'm German so I can explain it to you from a German point of view. The first problem is that, like in many other countries with many other languages, there are no words for content ratings. Literal translations of "General", "Moderate" and "Adult" don't sound like content ratings to a German, a Swiss or an Austrian. "Adult" means "grown-up" and only "grown-up" and nothing else. It refers to the age of a person or an animal or so. It does NOT refer to content. And it contradicts neither what "general" means in German nor what "moderate" means in German. The German translations of "general" and "moderate" don't contradict each other either.

In just about every other language in the world that isn't English, it's the same.

By the way, "Adult" is still "Adult" in the viewer if you set it to German, it isn't translated because that'd make less sense rather than more. It's "erwachsen" in Googlish, though. As I said, that means "grown-up". "Moderate" is "moderat" in both. "General" is "generell" in the viewer and "allgemein" in Googlish.

If you want to make clear in German that it's a content rating, you'll have to use USK codes (or FSK codes for those born before 1980). However, they don't really line up with American content rating systems, and neither really line up with the Second Life content rating system. Second Life Adult is either German USK18 or "banned in Germany". Second Life Moderate is German USK16, USK12 or even USK6 depending on the region, and yet, the region itself is always strictly 18+.

So much for the language, now comes the culture. Linden Lab's home is already somewhat liberal. There are much more restrictive and prudish places in the USA to the point where a little bit of visible areola is seen on the same level of naughty as hardcore porn and outright BDSM.

Outside the USA, it's more extreme. And I'm not even talking about places where women even have to fully cover their faces in public, lest they get sentenced to death. Not even Europe is as homogenous as some Americans believe it to be. In most areas of the world, nudity is a big no-no. The results range from being forced by law to cover up a lot to very daring beachwear that's just barely legal.

Denmark, in contrast, doesn't have much of a problem with nudity and allows public nudity as long as it isn't explicitly sexual. AFAIK, the same goes for the Netherlands. In Germany, public nudity is allowed a) as long as it isn't sexual and b) as long as nobody is disturbed by it, so it's slightly more complicated. But Germany also has a long tradition of nudist movements, especially FKK (Free Body Culture).

Now let's take this to in-world. A Dane may pretty well build a sim that's rather Danish in style, give it a General rating so that it's for all ages, but allow non-sexual public nudity everywhere. They won't be able to do that in Second Life, but in OpenSim, especially on their own grid, they can get away with it. It just mirrors real-life Denmark.

There's an actual Moderate-rated German nudist sim on the Hypergrid that both absolutely requires everyone to be naked and at the same time allows the presence of child avatars. Yes, this leads to naked child avatars. An American will cry out "paedophilia" and "child porn", as will people from other places in the world. Bad enough that a nudist sim is only Moderate-rated, it should be Adult-rated.

For a German, it's just your standard run-of-the-mill nudist camp. It isn't like kids must cover up on real-life German FKK beaches while grown-ups must not (FKK usually means strictly nudity as in you must NOT wear clothes). By the way, sexual activities are strictly forbidden on this sim, just like real-life FKK beaches and camps strictly ban public sexuality, just like real-life FKK fans never get tired of explaining that FKK is absolutely nothing sexual, full stop. Most people from outside Germany still won't get it.

Next, let's add rating misunderstanding to the mix. So someone from one of those more prudish places around the Mediterranean builds a sim. As for the rating, there are three choices: "doesn't sound like a content rating" (General), "doesn't sound like a content rating either" (Moderate) and "something with grown-up that doesn't sound like a content rating" (Adult).

The only reason to pick a rating, namely "something with grown-up that doesn't sound like a content rating", i.e. Adult, is to declare the sim adults-only and keep kids out. There's no other apparent difference between these ratings. Again, unlike an American, a French or an Italian or a Greek won't necessarily know by heart that Moderate is naughtier than General, and Adult is naughtier than Moderate. So they pick Adult if they don't want kids on their sim and randomly either General or Moderate if they don't care. Apart from the child avatar policy, everything else is strictly kept on the same level as General.

Add to this that not all grids are run by Americans. Even if they were, they'd still have different standards. Someone from NYC, Tulsa, Berkeley or Seattle would run grids on somewhat different rule sets. But someone from abroad may have even more differing rules and standards. The smaller the grid, the wilder the rules and standards can be, also because nobody can control a personal grid than the grid owner.

There's no stopping a Dane from declaring public nudity legal even on General-rated sims on their own grid. But there's also no stopping someone from completely banning nudity even on Adult-rated sims and redefining the Adult rating as "grown-up avatars only" but otherwise General on their own grid because that's their understanding of the Adult rating. And as it seems, there's no stopping someone from doing the latter on most public grids either.