They didn't early on, but I'm seeing it more and more now. Sometimes they even have "Rental" printed on the disc itself.
Oh, okay, that's what I thought. So my question is still unanswered.
One question that maybe can be answered, though: if one has a conventional, non-HD television set, the kind with a picture tube rather than a flat screen, would there be any visible advantage in watching a Blu-ray disc rather than a conventional DVD?