If you forget the DRM issue (which has restrictions regardless of manufacturer), if you keep everything in mp3 then it should play on pretty much every player under the sun. If you take the default formats for the iPod and many windows media based players, I'd far rather use the iPod and AAC since Apple don't own AAC - anyone can use it. Microsoft own windows media and have already abandoned one variation of DRM for it. The bottom line is that if you use an iPod you are in no way tied to it - unless you choose to buy songs from the store - which you don't have to.
In terms of movies, sure you have to convert them to iPod friendly formats but they're hardly iPod only, mp4/h.264 are (again) open formats and any player can play them if they wanted to. Apple choose not to promote things like xvid, divx etc for a variety of reasons. They have no control over xvid etc, if new codecs are required they have to make sure their users have them, they may be discontinued, whatever. Plus they feel h.264 is better.