The problem is that in Windows sometimes it is hard to run certain software programs without being logged in with an account that has full administrator rights. Chalk it up to poor design on the OS, the software program, or both. Everything is a holdover from back when Windows was designed for only one user, and that user had full access to everything. Keeping "backward compatibility" will be the death of the computing industry...

Also, this article only covers email viruses. It fails to mention the fact that without a firewall, your computer could become infected with a worm within a half hour of being connected to the Internet. It also fails to mention that other programs (such as older instant messaging clients, spyware, etc.) can open holes that could allow your computer to become infected.