Haha well, it does have more features than the rest, more filters and junk, but I tried a CS 3 Trial and I didn't really find much difference. Thing is for higher versions the more brushes you'll find. Before when I actually used brushes, for example it appeared "only for Photoshop 8 and up."
So ya, but the differences are slight from CS to CS3, although there's a big change going from Photoshop 6 to CS.