Upconversion CRT vs Plasma and 1080P

[Lagos55]

My previous television was a Panasonic CRT 34 inch HDTV tube. I noticed that there was almost no difference in PQ when I combined it with my Sony upscale DVD player. Did not matter if it was set to 1080i or 720p or 480p it all looked pretty much the same. I thought it was due to the fact that upconversion did not really work as well as most people said it did. However, when I got my new Samsung Plasma (768p) I notice that there was a big difference in PQ quality between 480p and 720P and 1080i. The 480P setting seemed closer to the quality I got with my CRT TV. And for some reason the 1080i gave me the best picture of the settings? Why the big picture difference. Why can'nt crt's upconvert properly?

Another question is about resolution. I know that most earleir 720p panels can not accept 1080p signals. My set actually does accept the 1080p signal. I was informed that most newer 720p (768p) TV's usually share the same processor with their 1080p counterparts only difference is that they have a 768p panel and programming to compensate for 768p. Is this true?