CNet reports that Oblivion get re-rated, because underneath all the clothes, the avatars are naked and a mod can reveal that.
You pretty much have to include a nude or near-nude model in order to have a good clothing system, because anything drawn onto the base model will show through when you do certain clothing types. You could, of course,go to the extra lengths to have alternate underwear sets drawn onto alternate base models, so that there’s always a base model to choose from that works with a given piece of clothing, but what an asset nightmare.
The real question in this case is different: why is Barbie-level nudity mature? Is the art on the base nude models not Barbie-level? If not, why not? If so, then what’s the problem? We give Barbies to very young kids with no qualms…