You've always been responsible for paying tax on mail order purchases.
At least in Kentucky, our state income tax form has a line for "use tax", which is essentially a place for you to pay sales tax you weren't charged at the time of purchase.
For a long time now, retailers with a physical presence in your state have been required to collect sales tax on mail order. Amazon was the big one since they're everywhere, but I've run into it with Best Buy, Cabelas, and a few others. In fact, it was kind of a big deal with Cabelas built their first physical location in Kentucky because of this.
A more recent court case required retailers to charge destination sales tax. Most big retailers started doing it late last year. Ebay has only started doing it in the last few months-Ebay itself collects the sales tax and remits it to the appropriate state. The seller has no involvement in it.