It isn't anything new. When you order something from another jurisdiction you aren't a simple consumer. You are an importer, subject to all the rule of any other importer. Amazon just implements what everyone was supposed to be doing already.

Allow online sales to occur without sales tax and one day nobody will ever pay sales tax. Every transaction could be structured in terms of online order and local delivery. Starbucks could let you order coffee online, then pick it up at the counter. This is why states are moving on this issue now. Amazon is just the first to implement it on their side of the transaction.