I think all the others have good points, but I figured I'd add another: Typically, at Arisia, there are several vendors who sell things that you don't really want to have out in a giant open space.

Sure, Arisia is a very open community, but I imagine some parents are thankful that they don't have to explain bondage gear or Hentai to their 3 year olds... Dealer's row has the ability to put things behind a door, or around a corner and have warnings, so you know what you're about to see...