Following Apple's announcement that they would be offering iTunes Movies for sale on the same day as the DVD release, they quietly added the ability to buy movies directly on the Apple TV.

Prior to this, the Apple TV could only be used to rent movies, not buy them. Instead, the customer would have to buy the movie on their computer and stream/sync it to their Apple TV. With the quiet addition of the "Buy" button, customers can instead buy movies directly from the Apple TV, which will later sync it back to your iTunes library. This had been a curious omission given that television shows and music could be purchased directly on the Apple TV.

It appears there was a glitch last month that caused the "Buy" option to appear briefly before Apple removed it.