Just a few days ago I talked about the way the digital age is changing the music business and how Aerosmith was able to sell three times the number of “Guitar Hero” games bearing their name than the number of albums their last release garnered.

A recent update from Harmonix, the developer of “Rock Band” reveals that the market for this new generation of music-oriented video games is bigger than some of us may have expected.

In the 15 months since “Rock Band” was released, the company has earned more than $1 billion in sales in North America alone. More than 40 million individual tracks have been purchased for the game. Clearly, there are quite a few plastic guitars in the hands of gamers across the continent.

Having personally heard a lot more about the “Guitar Hero” series of games which are in direct competition with “Rock Band,” I was a bit surprised to learn that “Rock Band” is currently the leader in sales. In fact, the game was “the number one title of 2008 by revenue across all game genres,” according to the press release.

Considering how big the video game market is in general (and with two teenagers, believe me, I know how big it is!) beating every other game across all game genres is no small feat. It seems that the marriage of video games and rock music is a match made in heaven – for wannabe rockers as well as the folks who had the vision to come up with the idea.

“Rock Band” currently offers about 600 tracks and is pitted against the makers of  “Guitar Hero” in efforts to ink new exclusive deals with artists for the rights to use their material.

Planned for September, the release of “Rock Band: The Beatles” may be a bigger bang (apologies to the Stones) than we’ve previously heard from this emerging industry. Someone, somewhere must be wondering if there’s room for more than two big players in this market, so who knows what we’ll see next.