I personally think the biggest problem at shows is sound bleed from other rooms, not to mention the general raised noise floor of hundreds of people gathered in a small space. Yes, I completely agree that hotel rooms are not always ideal, yes there may be other problems, but ultimately shows are inclined to be noisy places. Even a "quiet" room isn't nearly as quiet as you'd experience in a domestic environment. What hope have we got of hearing a system at it's best when competing with explosions down the hall?
The best show sounds I've heard have been when there's hardly anybody else there and the layout is sparse enough to allow some distance between rooms. Obviously, this is easier at a smaller-scale show in the likes of Dublin than at a massive industry even in Vegas, but it shows me that it can be done.
Well, actually the best show dem I ever heard was the PMC BB5/XBD speakers with a stack of Bryston electronics up the ying-yang, and none of the above applied to that. Not the last word in subtlety though...