Music downloaded from Sony's music store is in ATRAC format and are prevented from playing on non-Sony devices by Sony's digital rights management technology. It's also far more draconian in terms of what you can do with your music, with regards to burning CDs and converting to MP3.
LOL! what a ripoff.
(Yes, the above is true. IIRC, the Sony music store also costs more than Apple's. And looks like your dream of Sony coming up with an iTunes competitor just got flushed - Sony's only been trying since about six months after iTMS came online, and they're giving up. If *SONY* can't do it, nobody else is going to.)
Sony, will just make an exact copy of iTunes. Same format and everything but make it able to play on every device. Then Apple will die. :)