My definition of 'Dark Fantasy' has always been in alignment with what Wikipedia and TV Tropes have been, Fantasy with horror elements, such as shocking portrayals of blood/gore, and darker elements, such as depraved sorcerers, truly evil demons, the unpleasant aspects of human sexuality, and whatnot.
In that regard, Dragon Age: Origins certainly tried to approach that, compared to the squeaky clean look and feel of contemporary RPGs such as Neverwinter Nights, Eastern RPGs, Elder scrolls, and whatnot. Whether it's more 'mature' is an entirely different argument. Frankly I think Dragon Age could have gone a lot darker, the closest they got was how the Darkspawn Mothers were made. On the other hand, they were restrained by their rating, true Dark Fantasy would totally have gotten them a 17+ rating, impacting sales.
So yes, I would say that they failed to be a true Dark Fantasy, instead sitting uncomfortably in the middle of High and Dark. From the look of Dragon Age 2, and the upcoming sequel, I would say they are drifting towards High Fantasy as the overall tone. I frankly don't think there will be a good Dark Fantasy video game that is able to take the genre to it's full potential. It's too hard to chase the high demographic groups and really delve into the truly horrifying fantastical.