I am not a lens design expert but would agree with the theory that wherever there is some additional constraints in lens design, either price or lens quality has to suffer, or both.
I have a small and quite well made Voigtländer 15mm on my Voigtländer Bessa-L and the pair is light, portable, and fairly inexpensive.
A 15mm on a SLR would undoubtedly be more expensive, heavier, and very likely sacrifice some image quality on the altar of design complexity. I very often take pictures of architectural subjects so distortion correction is something I deeply like.
I would say that, overall, wide-angle photography is something that would better be left at range-finders. If you are the kind of persons that goes around with two or three bodies, the wide-angle body should be a range-finder (or quasi range-finder, like a Contax G2). It's not just a matter of distortion correction but also a matter of weight and size.