well to be fair, GTHD is only demonstrating this with one car on the track at a time. So there really is NO way to compare what would be possible in the other game if they focused all of their energy on that.
and by most accounts there are jaggies in GTHD too so it's not perfect compared to the other game either (which does MB and DOF in game; not just replays).... but the car modeling and lighting is out of this world from what I'm seeing from GTHD.
Like he said though, PGR3 is half the resolution (not even rendered in 720p) so the shimmering and jaggying is much worse I would think than GTHD which is at 1080p. Plus, since it only moves at 30fps, that MB (motion blurring) is a necessity whereas with GTHD, at 60fps, your eyes can blur that stuff for you (though they could most likely do it if they decide to).
Asides from that, this is a free demo of a game that isn't even finished.