On Windows from Vista and onwards, you have to press through an UAC dialog to perform something that requires admin rights like installing or uninstalling programs. On Linux to become root, you have to type your whole password.
Why is that? Why is there no passwordless sudo in any Linux distribution? Does the lack of password protection on Windows means that it is vulnerable in some way? If so, I'd like to see a proof of concept or a explanation of exactly how.
Update: Thanks for the answers, but they don't address my main question. To be more precise: If there isn't a vulernability in the Windows way, then why does Linux distros keep pestering the user to have to enter a password all the time? If there is a vulernability, then exactly how can it be exploited?