[Alastor]

I don't read/look at either, but I see this trend when it comes to fanfiction as well. Pairings and such, you know ^_~ and what I notice is, girls don't have this stamp of being sexually desperate nerds who don't really get much in contact with the opposite gender. If a girl creates Yaoi or Shounen-ai, it's commonly seen (I think) as simple daydreaming or minor fantasizing. IF a girl reads Yaoi or Shounen-ai, it's basically the same thing - not so much daydreaming, but kind of like innocent fantasies.

Now, let's look at boys here. There is a bigger chance that a boy who creates Yuri is seen as someone who simply wants to make his fantasies a bit more concrete (as opposed to abstract, which is what it is when it's in the mind). Unless they're tastefully and/or skilfully made, they will - to many readers/viewers - be perceived as nothing but sexual stories written solely for the pleasure of the creator himself. NOW, if a boy reads/views Yuri, a similar case follows. It's basically like watching Hentai, or something of the sorts. There are of course exceptions and this isn't ALWAYS the case, but it may tend to be.

I'm mostly coming from fanfiction here. If I were to draw Yuri, I would make sure that it serves the overall manga that these two girls like getting it on. If it's there just to get the sexual stimuli increasing, then I may as well draw Hentai.

That's my take on it, and I think many others here who have posted their ideas may very well be correct, as well.