I mean that most of the "important stuff" is running in user space. You can shut down the computer, spread viruses, and delete the user's most important files. The only administrator-owned files on a typical Windows installation happen to be the replaceable ones. The ones modifiable by a user are the custom, personal, and sometimes irreplaceable files.

This is mostly true on personal Linux machines as well. I'm just expressing my opinion that you don't need root access to pwn someone's machine.