Fenixp: Nope, you don't. You should find out how development works, because it's not that simple. The company is going to be sitting on the finished game for quite some time before actual release, and they can use this time to make DLC. What I do not like is that they refuse to bundle it with the game itself and make it some sort of "awesome special deal," it kind of seems like a poor deal when compared with, say, standard edition of The Witcher 2
Sorry Fenixp, but I have to disagree with you on this. The idea that developers get to spend 3 - 6 months twiddling their thumbs prior to a release is simply not true. I've worked on 'shrink-wrapped' released products (not games I admit), and the developers are fixing bugs and addressing issues right up to the time it goes to get pressed onto a disk (hopefully very minor issues by then).
I think what you mean is that the project becomes 'feature complete' at some point, and they then go through the hardening phase to actually ensure the features work (I don't know about games, but very few project managers would allow a 3 - 6 month hardening period, they simply don't understand what it is).
I suspect in this case the situation is more simple. The 'core' team would have at some point internally published a set of integration points. This would then have given the DLC team time to start writing the add ons while the game development was being completed. The DLC team probably has an entirely separate test team, and operates as a totally isolated team, viewing the core product as a black box.
So I'm afraid I have to agree with Roman, it would not have been the testing that stopped the product having the DLC included. It would have been separately tested in parallel to the core testing, and could easily have made it into the boxed product. I think there would be reasons such as accounting (the DLC team would not be producing any revenue if their addons were bundled), or simply greed, but not testing or development processes.