You are missing the point. Amazon got a tax break not available to their competitors like Barnes and Noble. Now they want sales tax imposed so that startup online firms will have a big barrier to cross.
There is another unexplored issue here in that both amazon and ebay facilitate on a major scale the avoidance of customs duty by their sellers/buyers. Many sellers will list a US ship from address online and then mail from say China. Product is mailed directly from china with a fraudulent customs declaration. Ebay/Amazon know this is happening on a major scale but do little to stop it.
If they are going after sales tax then absolutely amazon/ebay should be directly responsible for that customs duty. Put the heat on them for that and see what Bezos has to say.