car commercial music is often songs from real bands, or songs created to sound exactly like (without violating copyright) a particular song from a particular band. there's a commercial on right now (cadillac i think) that uses "stars" from Hum, which makes me feel like i'm 300 years old. i'm bracing for the day i hear a soundgarden track in a swiffer ad.
that said, i think making 30 sec tracks for commercials would be the coolest job in the world