I haven't upgraded to Tiger yet because it won't arrive from Amazon until tomorrow. But today Software Update on my Panther-running PowerBook informed me that Quicktime 7 was available.
Given that the Quicktime 7 upgrade is available for Panther, it isn't really accurate to say that Quicktime 7 is a feature of Tiger. It just happened to come out at the same time and so is bundled with it.
I wonder if any other so-called Tiger features will be available as free Software Updates for Panther users. I'm guessing Safari 2.0 or Mail might be another contender. Maybe even iChat AV.