Why would Amazon need an "excuse" to dump the affiliate program? I don't know how many affiliate programs I've been in that suddenly came to an end when the business no longer felt they needed them. That's business as usual in affiliate marketing, isn't it?
Mind you, I'm not sure Amazon DOES need the affiliate program, and I've been expecting it to come to its natural end any day now ever since I started making money on it. But for now, my guess is it's still worthwhile to them, but not at the expense of the accounting, administration and theoretical lost sales* Amazon would have to deal with if they complied with the states.
*I say theoretical because maybe it's just the area I'm in, but paying sales tax won't change my Amazon shopping habits a bit. Not unless the stores in my area want to start stocking a decent selection at affordable prices... which of course they won't.