You gave been GXified
Suppose you have five thousand songs in your library and you copy them all onto your music player. It takes several hours and it's done. Great. No iTunes required, simply copy-paste. You're very happy.
One month from now, you want to update your music player but you realise that you've deleted several songs from your player that you want again and you've added or deleted several songs from your computer too and basically, you want your music player to have all the same songs as your computer.
What do you do now, dude? Sort out all the different songs and copy them over and delete all the ones that you've deleted from your computer? It can take ages and can be very frustrating, specially given the fact that since you don't use any media management application, your collection is probably full of songs named "Track 01" and "Track 02", etc. and don't have the proper ID3 tags.
Or you'll just have to empty the whole player and copy the whole collection again, which again takes several hours. And what if those songs are spread all over the drive?
You see what I'm getting at? You see how a mediator like iTunes helps?
Winamp, WMP11, J River media center, Amarok all do it too. iTunes isn't the only one which can do this.
For example, all my songs have artwork associated with them, only because iTunes has Cover Flow. Why would I bother with it if I didn't have any incentive to?
WMP11 has no cover flow, still all my songs are 100% tagged. What's your point here, can only iTunes tag properly ???/