Ray, that's a good point. To corroborate this, on my Samsung HLN-507W 50" DLP, a well-mastered anamorphic DVD (720 x 480) looks to the casual observer just like true HD. Of course 720p is better -- it has 3x the pixel count at 2x the frame rate. But it's amazing how good even *current* DVDs can be when well mastered.
HD adopters quickly discover an issue all too familiar to Axiom owners: even on current 720p displays, there's a huge quality variation due to source material. Like Axiom speakers, quality is often limited by source-material, not the reproduction technology.
E.g, I've seen different shows, all broadcast in HD, that spanned a quality range from barely above analog NTSC to so clear it's like a picture in space. It all depends on source material quality and how carefully that quality was maintained during the multi-step transition to your HD receiver. A frequent pet peeve is when broadcasters use statistical multiplexing to reduce data rate, siphoning off bandwidth that subtly (or not so subtly) degrades picture quality.
It quickly becomes obvious to HD adopters that HDTV is more analogous to a very high definition version of streaming video on your PC. Many things can interfere with the data rate needed for true HD.
Like Spiff said, thank goodness for DVDs and soon-to-be HD-DVD.
