From wired.com, this article by Eliot Van Buskirk: "Products Placed: How Companies Pay Artists to Include Brands in Lyrics."
Here's the punchline:
"things have gotten so weird in the music business that high-profile acts are inserting ads into their song lyrics. The next time you hear a brand mentioned in a song, it could be due to a paid product placement. And unlike magazines, songs are not required to point out which words are part of an advertisement."