Well the whole thing doesn't make sense, so it's hard to understand. Yes, the digital deluxe edition will come with Warden's keep, but only because you're already downloading the whole game, so they can easily throw in the extra download. However, it's essentially separate content because people who bought the full, retail collector's edition will still have to spend the extra $7 dollars for the DLC.
Dragon Age: Origins DLC details and limited-time offer - Neoseeker News Article
BioWare Plans Years Of Dragon Age DLC - Dragon age: origins - Kotaku
The two free, included DLCs will be free to anyone who buys the game retail in the first 6 months. I suppose they see it as something akin to royalties. Even, if people buy the game used, years down the road, they still can cash in on the DLC.
They also want to control the game experience. They'd like you to always be excited for the next DLC and I suppose tell them what you want so they can incorporate it.
I'd like to say you have to option to use community content only to control your own game experience, but they will probably release some must-have, game-changing content only available in the continued DLCs.