Everyone is required to pay sales tax for purchases made over the Internet, there's just no way for the states to enforce it. That's why most state tax forms now ask you what purchases you've made online so they can add that into the tax. If you don't answer this question truthfully, then your liable for tax evasion.
So the real question is should they continue to enjoy this oversight.
I suppose the eventual taxation of all online commerce is inevitable.
Seems to me that if the present conditions continued, eventually tax would be forwarded to carriers(UPS,FedEx,USPS). Maybe this is pessimistic but I see all online purchases being charged sales tax in the future. Of course, the bureaucrats will have to set up some system for that, which will take years if not decades.