Cause they stated themselves that they haven't said anything about Retribution being the last expansion. But there is a chance that after its release they might work on it. I haven't really heard anything about DOW 3, and i doubt they're working on it since most of them were probably working on Space Marine. If I remember to get screenies of them I will put them up, but Winter did you hear what THQ was doing for DOW3?
They are an unusual chapter in that they have an excessive amount of turtle wax.