Are women incapable of understanding that people can be a-holes especially in an unregulated "sporting" competition? Lots of a-holes out there. Just put a warning, let women know, and offer advice if necessary. This is just plain ol' wrong.
I think they are fully capable of understanding. But I can guess that the LAN party probably gets tons of complaints regarding assholes and women every year and just decided to put a stop to it.
Just look at a site like Reddit (which probably is the same demographic as a LAN party). As soon as a women appears, the assholes come out.
It's EA so I'm already boycotting it. :P