It occurs to me to add that this problem is so far off the radar of the average American that it isn't even an issue. A lot of people want a crackdown on illegal immigration, and a lot of people want better controls on who's coming in on visas, but there's no public perception associating that sort of thing and musicians being kept out. As long as Eric Clapton and Bono and big-money folks like them are getting their visas, the vast majority of people don't even notice that there's been a change. The US folk press has written about it, but who reads "Dirty Linen" or "Sing Out"?   :-)

The irony is that the musicians being hurt are the ones who try to follow the legal procedures for performing over here. The ones who just come over on tourist visas and then, uh, happen to do a show or two while they're in the country escape scrutiny unless they happen to get caught.