I'd also imagine there's also the longetivity of the show. You see what happens in a show like The Producers when the original cast leaves, Avenue Q was able to do a great job avoiding that fate. Now imagine if the part of Gary Coleman was played by Gary Coleman for the first year. His contract ends, he leaves, now what? Do you have someone else play Gary Coleman, which would now be weird to everybody? Or do you Weissler it and, depending on when you see it, you'll find Zach from Saved By The Bell living on Avenue Q this month, and Balkey from Perfect Strangers next month, and Brooke Shields living on Avenue Q in December, and then what happens when Gary or whomever is out sick or on vacation, you can't make sure every understudy is also a has-been celebrity... all seems quite expensive, and it all sort of ruins it for any future amateur productions in that the show hinges on having semi-famous people in it...
- Gil
http://www.broadwayabridged.com