I admit the comparison is more sensationalistic than informative; the differences in the market for digital media distribution from 2003 to 2008 are vast. However, the numbers remain impressive, and this perhaps signals the beginning of a heyday for DLC.
With Nintendo considering microtransactions for DLC on the Wii, Steam and Xbox LIVE opening up to independent publishing, and the potential features the PS3's Home and associated content stands to bring to the table -- nearly all of core gaming is rapidly adopting DLC as an essential part of the gaming experience.
Harmonix's success in this area shows that the model is a viable one, and that as publishers adapt to the marketplace, we're likely to see increased quality in the offerings for downloadable content.
This is all good news for advertisers, too. As a networked connection becomes increasingly necessary for the gaming experience -- from multiplayer gaming to access to additional content -- the reach for in-game advertising will continue to grow, and opportunities for brand tie-ins will increase.