At the moment I have 8816 songs in my iTunes library, and iTMS hasn't even opened here in Norway (if it ever will)...
Just think of iTunes as a jukebox on your computer, you fill it with your favorite music, ripping your own and close friends and relatives CDs, <coughing>whatever mp3s you have lying around</coughing> and top it up by adding songs form the integrated online music store cheaper than buying CDs. You organize playlists whith your favorite tunes, sync with your iPod and/or burn CDs with one click... what else is there to want from a music player... No other music library/jukebox program comes even close to iTunes when considering ease of use, style and price (it's free, after all 😉) for Windows or Mac OS X.
...iTunes was like a wet dream for me back in the 80's when I spent countless hours compiling mixed tapes from my vinyl albums, when I started using it a couple of years ago it just made sense, this was what I'd waited for... 😉