It sounds as if the tax-free holiday we’ve enjoyed on Amazon.com is about to come to an end. Someone from the Texas comptroller’s office — which handles statewide sales tax collections — apparently found out from the Morning News that Amazon.com has been operating a distribution center in Irving since 2006, according to the Morning News, giving the retailer a "physical presence" in Texas, which is typically the test by which the state determines who should be paying sales tax on sales and who is legally allowed to skate. The News story says Amazon.com didn’t respond to calls, but this is a huge deal: Oftentimes, the biggest different in cost between buying something from Amazon.com and, for example, buying it at a Best Buy store is the sales tax. If Amazon.com, and eventually all online retailers, lose that advantage, it will change the face of internet shopping; the story points out that the comptroller’s office believes the state lost $541 million in sales tax revenue from internet retailers in 2006.