Vista did add some prompts for things that an admin could do that really shouldn't have resulted in prompts. What actions that a limited user could previously perform resulted in the new prompts?
The first thing that comes to mind is running regedit. Despite the elaborate ACL system in the registry windows won't run it without admin rights. You can still use any other program including reg.exe to access the registry, but not the convenient one.
Did it work pre-vista? If so, I agree that's kind of a lame change. It seems like a pretty minor issue in the grand scheme, since generally users shouldn't be mucking around in the registry, but it's lame nonetheless. I assume that if it worked previously, it was decided that the effort to implement key-specific UAC was just too high, so they implemented whole-app elevation.
Note that there is no security need for admin here, just a dumb prompt that you can't second-guess.