Guys just don't open up as much. Personally I've seen a lot of guys I thought "dam that's a nice set of abs," though it was more of an "I want mine like that" then something to do with me liking the guy in some other way. It's all dependent on who the person is, and how they open themselves up. As for girls expected to be more open? Well they just are, so that's how its going to be until you see more guys home cooking and watching their kids then woman. Which wont happen for a while, its just how we were organized in this crazy world, go ahead and try and change it if you dare.
Hmm, well I disagree with a lot of what you said but please do not take what I am about to write offensively. I think the new "expectation for women to be bisexual" is socially a very new element of American culture- other cultures have had it longer (ie Japan) or not at all (ie Latino culture). I think this has very little to do with women being more expressive than men, although they are indeed encouraged to be so in our society. Instead I think that this can be largely attributed to two other factors--
First, the prevalence of queer women in American pop-culture. Before the '90s there were few if any "out" women in the limelight. Indeed, an expression has occurred in lesbian culture referring to this- "After Ellen". With more queer women in the public's mind, it makes sense that queer women were in fact thought about more often. Of course, the same can be said for gay men in the last ten-twenty years, so obviously this is only part of the cause.
The second element here is definitely up to interpretation, but I attribute it to the prevalence of "lesbians" in heterosexual pornography. (I use "lesbians" to refer to depictions of women who are described as lesbian but who actually behave as bisexuals.) With being queer becoming increasingly socially acceptable and with lesbians already being so heavily sexualized, it was a natural progression for lesbian-fetishists to take it one step further and begin suggesting to women that they /should/ be attracted to other women, rather than /could/. This was no doubt re-enforced by songs like "I Kissed a Girl", which we briefly touched upon in the panel.
Returning to the question "Why are women expected to like yuri?" and the response "Men are less expressive (and the conclusion that this will stay the same until men "cook and watch after children more than women")": Interest in yuri is unarguably not mainstream, especially non-hentai yuri (hentai itself couldn't be construed as mainstream), so there cannot be any special clause in American consciousness for it. Instead we are seeing a separate but connected phenomena adapting to our own specific subculture.
As for camname21's response, I find myself quite bothered by his underlying assumptions because they would mean that, if they are true, America is still unwilling to accept male homosexuals. However, within our own subculture there is proof that he is at least partially incorrect-- yaoi is consumed almost entirely by women so the sexual interest in opposite-gender homosexuals definitely exists in females as well. And even more conclusively, I have certainly had self-proclaimed "yaoi-fangirl" friends who are /constantly/ trying to pressure their friends into yaoi, regardless of their gender or sexual orientation. I think the lower proliferation of this can be almost entirely accounted for by the greater acceptance of lesbians in comparison to gays in American society.