Actually, I'm pretty sure you're wrong about companies selling this information. Smaller retailers manage to avoid this hassle by... not having to pay sales tax for out-of-state purchases.
That might be whats behind Amazon's change of heart. This will be difficult for them, but its probably impossible for smaller retailers. It might be expensive in the short term, but it protects them from competition in the long run.
I think GP was suggesting that there is at least one company selling software that will allow you to compute sales tax on an order, not that companies are selling their order book to states for the purpose of use tax enforcement.
That might be whats behind Amazon's change of heart. This will be difficult for them, but its probably impossible for smaller retailers. It might be expensive in the short term, but it protects them from competition in the long run.