Yes, it's same rules. Personally I wouldn't count breasts or bums as nudity. It's all pretty soft isn't it? However, you need to take several other things into consideration.
1. We have to comply with the rules of the hosts, so why push the limits and risk the board?
2. There are quite a lot of very prudish people around who get offended easily. Why risk upsetting them? It only creates a hard time for me when they start whinging and moaning and I like an easy life
3. People want to surf at work maybe, so why make their life hard by posting risky content, even in an avatar.
I'm sure, if you think about these things you'll see that an innocuous avatar will be a better choice.
To be honest, I've got more probems with people uploading massive avatars which are really wide and mess up the display. This is really dim behaviour. It tells you what the limits on size are when you upload your avatar. These limits are there for a reason, not just to pass the time of day.