Also, from a personal perspective, it makes the assumption that all the male coders in the room are straight, which is in some ways an even more insidious assumption.

You can look at the room and say "okay, sure, there are no women at this event". You can't do that with sexuality -- but people do anyway.

(I feel I should note that this unfortunate, embarrassing incident aside, Yahoo is an incredibly, almost ridiculously gay-friendly place to work)