Since you brought up the component cable issue, roger1818, I have to tell this story.
I was in a Costco store and a fellow working in the TV department there told me that upconversion doesn't work on any TVs. I knew that an HDMI cable is required for upconversion to work but thought he'd better learn that for himself, it's not my job to educate the folks that should be educating the consumer, LOL. So I left without mentioning a thing to him. Of course, like you stated many stores only use component cables, and Costco is one of those.
I have to admit I did not check the cables that Future Shop was using, I just assumed that type of place to be using HDMI cables at least for 1080p sets, since component cables only go as high as 1080i. Also, if they did use component cables for everything, like Costco does, the 1080p sets should still look better than 720p sets, since 1080i displays more pixels than 720p. But, your point about other factors affecting picture quality is well taken.