The best attended house show tour was their first one over here - I went to the Coventry one, it probably had about 3,500 there. I don't think they get that in the US. And if they do, they're doing it as once in a blue moon, not every weekend. They don't venture up into the northeast very often as that is WWE/ROH territory...
WMG - what it 'can' hold, and what it 'does' hold are very different - according to The Observer and Power Slam magazine over here, average attendance for the shows is 950-1000. Nobody pays. Just get into Universal Studios, and get a numbered raffle style ticket from the guy by the Jimmy Neutron shop. Return at 4pm and they start forming lines based on your ticket number. They let you in about 30 minutes before the show starts (although I havent been since they relaid it out last summer).
Bischoff is a businessman. He underpays everyone he thinks he can get away with doing it to and saves his money for "celebrities" - see underpaid crusierweights and main eventers galore in WCW while Master P picked up almost a million per episode, and Leno and Rodman main evented PPV's.
An outdoor PPV - TNA Road Wild, anyone? Uncle Eric does love his bikes...