I completely disagree with the idea that this is a sexist pressure. It's a "good looking person" pressure if not just a comic book pressure.
This guy basically says that even though I (a guy) haven't yet played FFVII that I should still be able to dress up as (what's the main character's name? I think Squall's the bad guy...oh yeah) Cloud without anyone putting me down for not knowing the character. Wrong, I should absolutely know the guy I'm cosplaying as.
Scenario: If I walk into Comic Con dressed as Cloud, big sword and all, and I'm dressed up really well, but don't know the backstory at all, I'm risking people getting really excited over my cosplay but then getting really annoyed after they start asking questions or trying to relate to me over the character/the game.
And here's a big point: cosplaying is COStume PLAYing. You're expected to act out the character. If you know nothing about Wonder Woman's personality or even the slightest backstory, then by definition you're going to be a terrible cosplayer, regardless of how immaculate your costume is. The exact opposite of your argument is true--you'd be a great costumer but a half-baked cosplayer.
Back to the whole "good looking person" pressure thing. If the woman wearing the really great costume is a nerdy woman and not some super hot model, she's going to get a lot more (legitimate) compliments because people will assume that she knows the character. Same with guys--if it's a really good looking guy, you're going to second guess yourself that he actually knows the character he's dressing up as. But if the guy is nerdy, you bet your bottom dollar he's got all the comics and seasons on bluray.
It's a hot looking person pressure because nerds are the outcast group. In response, we've made our own world, but it has gotten popular, which is great--except now the non-nerdy crowd tries to schmooze their way on in without knowing or caring about the mediums at all, and then they get offended that they're being called out on not knowing what the heck they're dressing up as. It's as if they're just trying to show off their hot bod--male or female--and they're there for nothing else.
NOT EVERYTHING IS AN ATTACK ON WOMEN. Please get over yourself and critically examine the situation. Draw a few punnet squares. Get dirty into the scenarios. Don't take the easy way out and assume things.
I understand that hot people can be nerds too, that's my whole point--that it's unfairly classifying hot people as unknowledgable regarding their cosplays. it's just not a sexism issue.