I think they only did that with 10.3, I had the same problem going from 10.2 to 10.3. But after 10.3, they have been full install disks. On the other hand, we were installing them on Apple Hardware, right? Which means that if the "original media" is OSX based hardware, Apple *could* claim that the disks were "upgrades"?
I'm not a lawyer, and don't pretend to play one.