Chris
Let's put it this way.
If someone buys a computer, and one wants to use it as is, fine. One's computer power will be just limited.
If someone wants little bit more out of one's computer, he/she has to keep computer updated. That includes plugins.
Secondly, Firefox works in different way, than IE.
IE comes with bunch of stuff, you like, or not. You can't even uninstall anything.
Firefox comes as a base. You want to make it better, you have tons of choices. That why, I like Firefox.
Besides WMP is M$ application, and it took quiet a battle to force M$ to issue .wmv plugin. It couldn't be done without M$ approval.