I am always struck by exactly how ignorant many gamers are of how game or software development actually works. Let me try to explain this for you all:
First, any studio-developed game has a set time limit and budget for development. This should be common sense. All of the time that artists, writers, voice actors, programmers, and QA testers spend working on content is time that they are paid for.
Because of this, there is a set amount of content that can be included in a retail game (which pretty much has a fixed price). This is typically decided early on, and as the game development progresses things are added and removed depending on the difficulties the developer encounters. At each point, a decision is made as to whether X feature is important enough to increase the time/cost of the game development - if it's not, it can get cut from the game. Many of these features might be very cool, and developers can be sad to see them cut, but this happens with every game.
At some point in the development process, the designers have to stop adding new features and content. At this point, the programmers and QA become very busy testing, optimizing, and porting content. In the past, this is the stage where most of the writers, designers, and artists either get fired or get moved to another game.
Instead of firing the content creators, many newer games are deciding to instead have them make more content, to be tested and released separately from the game as DLC. This does not mean that the time that is used to create this is free, or that it is a part of the retail game. In some cases, the designers go back to stuff that was cut from the original game and rework it and fix the problems, because they really didn't want to see it removed in the first place.
While this is happening, the final "gold" version of the game is created. This is the version that first needs to pass the console manufacturers' certifications, and then need to be sent to manufacturing. This can take several weeks. During this time, the programmers and QA can test the DLC content that the rest of the team had been working on. Because they're working off the final version of the game now, and this is just extra content, this process goes a lot faster. It is easily possible that digital content can be tested and ready to be released before the retail versions of the game are even done being manufactured.
But all this time isn't 'free' - the assumption that the people working on this content would otherwise be being paid to add things to the retail game is just stupid. That game development time and budget has already been spent - they would either be working on something else entirely, or looking for a new job.
To create this new stuff, it has to be paid for somehow. For The Stone Prisoner, it's being paid for to see if it helps make up for used game sales - a particular problem for a mostly-linear story-based RPG. The Warden's Keep content, on the other hand, is a marketing promotion to sell the more expensive digital collector's edition (sans cloth map). If you aren't 'paying' for the content in one of those two ways, then you should expect to pay for it directly.
