You could just as easily explain the failure of those shows this way: they were both boring. Caprica at least had a germ of an interesting idea and some very good actors, which is more than SGU had, so I cut it some slack but I don't expect everyone to do the same. Both deserved to fail on their own merits.
As for "proving" that they're boring, well, they bored me. They bored other people, who announced their boredom in the threads and then vanished. I think that's probably a sign of something.
Name a good show skiffy has done recently that was prematurely cancelled and didn't deserve it. This is a trick question because all their recent shows have sucked except BSG, and that one really needed to go after four seasons. Until skiffy actually airs a show that deserves to survive, it's impossible to say whether their bungling is hurting the shows at all.
The last show I can think of that definitely deserved to survive was Farscape, which was an unusual case, and after all, it did come back from premature cancellation for a very satisfying wrap-up. The quality on that show was very up and down, and by the last season there were more downs than ups. I'm not sure I'd have wanted another season from it, either.
I don't doubt that many people did find it boring, and I don't discount that as reason for fewer viewers, I just think there there are other reasons too, and were it not for those it could have survived.
All I know is, something was off. My friend who never watched a Stargate in his life was hooked on SGU. That was the mythical new viewer that SGU tried to reach, and in my experience did reach. Perhaps he was the only one? I don't know. I hope not, but the picture SyFy paints is a pretty sobering one.
I post on the IMDb forums and there are a lot of fans of SGU who were never fans of the other show, there are just not enough of them it seems.