The process of shipping a game is a gradual series of hardening and locking down. The world needs to be solidified so that the plot structure can be formed. The plot structure needs to be solid so that the plots can be written. The plots need to be written so that they can be scripted. The plots need to be scripted so that they can be tested. The plots need to be tested so that they can be voiced. The plots need to be voiced so that they can be staged and given cinematic polish. The cinematic polish needs to be finished so that it can be tested. Everything needs to be locked down so that performance testing and optimization and eventually disc layout and certification can be done.
Now, things dont always work perfectly, and changes often have to be made to things which were assumed to be locked, which causes a ripple effect and lots of work for everyone. You need to stop changing things at some point so everything that depends on them can be done. DLC is a separate product, so it doesnt have to be tested and verified as part of the final build, it doesnt have to be accounted for in the disc layout, and it doesnt have to be in the game when it goes through official certification. It has its own schedule and its own verification process. And lets not forget its own budget, because ultimately games are a business and manpower is limited by money.
To make the console ports possible, the content of Dragon Age was locked down in the spring. It wasnt possible to add new content past that point, and the VO lockdown was much earlier than that. The game was still tested and improved with bug fixes, stability and performance improvements etc, but adding whole new adventure like Wardens Keep? That would have pushed the release date back. The PC version had a very long time after content lockdown for testing and final polish, which could have been cut short to ship that version earlier, but it was decided to ship it simultaneously with the console versions for a variety of reasons. But thats a separate issue.
Could we have taken people from the DLC team and put them on the console version to speed the porting process up? Not really. Porting content requires a lot of programmers and not very many designers. We had a surplus of writers, tech designers and cinematic designers and even artists, so we put them to use. If anything, DLC is taking away from potential future projects, not from Dragon Age: Origins.