the scale & genie effects apply towards minimizing and maximazing a window...has nothing to do with the dock...so try both with minimizing something and you will see the difference...
Also, if you hold shift while minimizing, (or any of the effects such as expose, dasboard, min/maximizing) the animation will play back slowly and you'll really be able to see what each does visually.
I think whats great about the genie effect is that it help the user "understanding" what is going on with is window. I mean, for anyone who is really not into computer (see : my mom), the genie effect make the fact clear that the window you minimized is now "waiting" in the dock.
That's the purpose in general of having a great visual desing. Effects should not be put here simply to look cool, they should help informing the user on what's going on.
i've had computer illiterate friends love OS X for features like those.
when they minimize a window, with the genie effect, the can actually see where it is for when they need it later. something as simple as that makes their whole experience better