That is actually true, but it isn't by a large margin. There are new lighting effects, and the water graphics are amazing. Although it does have slow down at time (not choppy or anything, but not silky smooth like it normally is).
A few days before playing Ratchet I was thinking about Mario Galaxy and the thought of "Do I really care if Nintendo games were in HD with PS3/360 graphics?" crossed my mind. After playing Ratchet, I realized how much I want a Mario and other Zelda games in HD with good graphics and all that.