Windows does not and has not ever provided an uninstaller outside of their own software. It's just a place to look at installed/registered apps.
I'm not sure I want Apple adding a registry, or another database to my machine; do you want more artifacts?? Once you do this, you are requiring all developers to write to it, which isn't going to happen (certainly not out of the box). You do have to actually install to the Windows registry. I could certainly write a program which does not register and just leaves all sorts of files around your machine, about which Windows has no idea. This item WILL NOT show up in the add/remove list. Now you're back to the same problem all over again; this is all about the developers.
Frankly, I'd rather deal with manual uninstalls rather than a Windows registry. Windows registry is also why an installer is required, whereas we just drag and drop in X (don't need to script any registry entries).
I really just want good installer/uninstaller apps with the applications I choose to install, as necessary.
Then again, after looking at the Time Machine in Leopard, I wouldn't be surprised if Steve™ could figure out an entirely new and superior method.
Forget the Leopard Bells and Whistles, Just Give Me an Uninstaller