That does raise an interesting issue: if RB and even GH are raising significant amounts of revenue simply through downloads, what are the incentives for new releases?
You get a boost in game sales, from both previous users and late hardware adopters who will probably buy either game as an initial purchase.
Visibility of releasing a sequel due to constant press/media coverage.
New characters, venues, etc. could all be added through DLC, so presumably the next iteration of RB and GH will have new play elements, modes, etc. to push previous owners to buy the new version. It's not like the release of RBII or GHIV will keep anyone playing RB or GHIII from being able to purchase additional songs.
Regardless, there will be new versions in the future, the DLC just provides a constant refresh of new content to keep interest up. They'll make them simply because they'll sell, just like the 50 iterations of DDR that have popped up over the years.







