One time when I attended WWDC all the food served was vegan at the main social event. The impression here is Job's food preferences filter down as a mandate for all. At least in this instance.
OMG, I remember that year! It was even worse in 2003 when they moved it to Moscone. Fresh made Jamba Juice and mounds of Krispy Kreme donuts galore. It was super gross to be honest. :-) I haven't eaten a Krispy Kreme donut since that year.