You can also bet your ass that states like New York and California are trying to craft ways to "recapture" revenue from people who flee to other states. Rush frequently mentions that he is audited by the state of NY every single year, even though he has not lived there since 1997. He has to provide all sorts of evidence that he does not maintain a residence there.
The actual outcome of things like audits is secondary. As Mark Steyn has put it, the process is the punishment. The state drags people through proceedings, and even if the court decides against the state, the procedural agony is often enough to ruin people. It's part of their effort to beat people into submission, to fatigue them with unending minutiae and technicalities, and nearly all of it comes at bureaucratic whim rather than by statutory process.