"laws of individual U.S. states don't even apply across their borders - thats why states are able to *not* charge sales tax for purchases made from outside their own borders."
Umm, no longer true. Several states now have laws requiring out of state merchants to collect sales tax based on the consumer's residence and remit those taxes to the state of residence. Just check the order form in any mail order catalog you receive. Border towns often require the consumer to show his driver's license or other proof of residence before the sale is made.