Monroville said:

There is a BIG difference between DVD and Blu-ray (450i/p compared to 720p/1080p). Granted, it helps that you have a 50 to 65 inch HDTV (or bigger), as Sorcerer is kinda correct at least when it comes to smaller screen sizes (30" and smaller).

I believe Choice Magazine determined that 42" is the smallest TV where BluRay makes a noticabe difference at a comfortable distance. It also depends on the quality of the TV; I've seen massive TVs on display at electronics store that are playing DVDs, are connected by composite (not even component) via a splitter/switcher, and look absolutely amazing. I specifically look for signs of MPEG artifacts, pixelation and such, and have to look really close at good quality TVs to notice anything like that.

In contrast, I see plenty of MPEG artifacts on good signals of HD digital TV broadcasts. Maybe the TVs are not as good, or maybe it's the encoding variant.