Well, it is obvious that between a RAW file and the final image there are a lot of complex processing steps. But that is independent of the file format used. DNG isn't so much different, just documented. And while the manufacturers converter might give the best results, the photographers rather use the image processing programs from Adobe or their competition which use their own RAW converters anyway.

Yeah, they could do it with DNG (I suppose), but they don't really have any reason to do so (in their minds). Personally, I like open stuff, but they did not share my mindset, and I respected their posture.