if sales are indeed down, my guess would be that the focus of the show and majority of attendees are there for the pop culture/non comic book stuff.
i know if i was still actively collecting, i wouldn't want to wade through 124,000 (of the 125,000) attendees to try to find golden age comics that would likely be a bit pricier than normal because of table prices, travel, etc.
the fact that the focus has shifted away from vintage comics has convinced some long time comic book collectors (some of whom have posted in this thread) to skip it as not worth the hassle. i'd be in that boat.