Want to make a fortune in the music business? Get your song featured on a music-oriented videogame.

Collectively, the games Guitar Hero III and Rock Band have sold a staggering 7.5 million downloadable songs in just three months (two for Rock Band), with tracks selling for 99 cents and up. That's a level equal to seven times platinum.

MTV, noting that only about a million copies of Rock Band itself have been sold so far, said that the numbers were surprising. Says an exec, "We live in a rough time around music where our audience struggles to pay $20 for a CD but don't hesitate to pay $50 for a game. The notion to pay 99 cents or $1.99 to have a song and repeatedly play with it apparently isn't a big hurdle."

And there's the rub: Once you've spent $50 (and in fact, in the case of Rock Band, it's more like $170), adding another buck to the investment is virtually meaningless. It's a clever trick of the mind that convinces you that somehow a 99 cent song is worth more after you've already invested a lot of money beforehand than, say, just buying the same song online without a prior involvement. (Of course, the Rock Band track also comes in the form of a playable game.) The proof? The hottest Rock Band tracks are selling only a few hundred extra copies from services like iTunes vs. hundreds of thousands of copies in game form.

So what are the hottest sellers? For Rock Band, a Metallica pack including "Ride The Lightning," "Blackened," and "And Justice For All" is the top-selling download. Surprisingly, the best-selling single is Foreigner's classic rock jam "Juke Box Hero," followed by Creedence's "Fortunate Son" (a cover version), Weezer's "Buddy Holly," and "My Sharona" (also a cover).

LINK: "Rock Band," "Guitar Hero" drive digital song sales