I would say if you want to buy bulk Ammo your probably right. Those deals are way better on the internet for sure. Maybe one big dealer will have a good deal on bulk like your saving shipping cost. If you figure your gas , admission and packing it a country mile did you really save anything. If you looking for something old or odd this is the place. Not saying you won't have to pay up for that item but ally of these guys don't sell online so you can find things that you won't see anywhere else. A few years back someone had crates of Romanian pellet rifles for $15 ea. I bought 5 and I wish I would have bought a whole crate full.
And I'll add that when it comes to bulk ammo, you can still (or could, last time I went) find some bulk milsurp ammo like 8mm Mauser for less than you can find it (if you can find it at all) online. When it comes to "modern" ammo though, you're absolutely right. Probably as cheap or cheaper online. They often have crates of Yugo Mausers and Mosins too, although I'm not sure what the prices have done at the show for those. They used to be pretty reasonable. It's been a couple of years since I've gone.