It's the wave of the future. Been true for lots of purchases where the company "did business in" the state; I've always had to pay DC tax when I bought TurboTax or Quicken directly from Intuit, and the same was true with Symantec.
Why should internet sellers get a break that local retailers don't? They can always offer a better price because they save by not having to pay for brick and mortar; let them compete on that basis.