I think this touches on issues of prudishness and cultural "puritanism" that probably cross into a political discussion not entirely welcome on these forums.
You're probably right, but I would like to note that any actual prudes wouldn't discuss the subject at all. No one here actually seems embarrassed by the topic, or outraged that the question was asked. So any charges of prudery that cast differing opinions in pejorative language would probably violate other terms of discussion on the forums at least as fast as discussions of social norms raised political problems.
I think its shameful that the human body has somehow become not "family friendly."
Speaking as someone with a family, I found it interesting how quickly the kids decided that displays of affection by their parents were gross without any apparent indication of needing to be taught that. I can speculate on a variety of biological advantages to that being instinctive, though actually performing controlled research with children would be really difficult and I don't see an easy way to test the theory.
And while standards and conventions regarding what is modest vary between cultures and within cultures by context, I know of know widespread culture that espouses no standards of modest behavior. I don't think the issue is so much that the human body is not family friendly - almost everyone with a family got their family in the same way - but that everything has an appropriate context. People can be perfectly happy with presenting the human body in one context - say swimming on the beach - and still feel its display in another area inappropriate. I suspect that much of the opinions evidenced here regarding artwork in an RPG book are some sort of variation on that. I don't think that 'nudity is seldom appropriate' is the same as being prudish or Puritanical (leaving aside the fact that the maligning the Puritans as prudes is based on ahistorical slander).
And regardless, standards regarding modesty tend to be very personal, and as such it is very hard to transgress in common areas without offending someone. It's just a bad economic risk.
As far as my personal taste, I tend to see artists wanting to use nudity as adornment, rather than because its necessary. And while that's probably occasionally appropriate - I'm not upset by the Sistene Chapel as an obvious example - my experience is that a little goes along ways and most of the time its just a cheap gimmick. Dress your art in too much of that, and pretty soon that's all that people will see. The literary equivalent occurs all the time. I don't know how many really interesting sci-fi and fantasy novels I've read that were discussing a wide variety of topics and ideas, and developing setting and character, and then the author has his many characters in an explicit sex act and even if the scene itself is well done after that it's like the text is lobotomized and all these formerly interesting characters spend the rest of the work obsessed about whose body parts are touching whose body parts to the detriment of the story. It's not merely that you may distract your readers; the bigger danger to the artist seems to be that they distract themselves.
Another equivalent is the use of profanity. At times, it's almost essential to a good text ("Frankly my dear...", "I want my father back..."). But I find that the temptation to sprinkle your writing with profanity is far more debilitating than attempts to avoid it. Eventually you impoverish your ability to express yourself, resulting in terrible writing. I'd probably stop reading after a while an RPG liberally laced with profanity, even though I'm sure few terms therein haven't escaped my lips at times.
So sure, I'm not saying that nudity would never be appropriate, any more than profanity is never appropriate; but I think you better have a very good reason.