Oh I can tell the difference. Hell, Final Fantasy XIII on PS3 still technically runs at 720p, but I still consider it one of the better looking console games just because it does such a good job of upscaling to 1080p. I also noticed the difference when I first hooked up a 360 to the same TV and set it to upscale all games to 1080p, even though they weren't actual 1080p.
I don't know what you're experience is, but I'll go off on a limb and guess that you've seen barely any games at all actually running at 1080p on a television, at least not any games with full 3D current gen graphics. Kinda hard to tell the difference when you haven't seen the difference. When I hooked up my computer to my TV just for a little trial run I was blown away at the difference, finally seeing what games like RAGE and Crysis 2 running in native 1080p at 60fps. I immediately thought to myself "this is what HD console gaming should have been."
I've got some PSN games which are in 1080p and I do *sorta* notice the added clarity. However, it's not enough to make me beg for it at every turn, and I'll never prefer it over a solid framerate for fast-paced games. Most of the time, I'm too into the game to be bothered about how the pixels could be a third of a millimeter smaller than they are. Also, I'm starting to get up there in years and my eyes aren't what they used to be, lol.