It's all about convenience. They might not be true barbecue, but they're much easier for most people to execute (par-boil and finish quickly with sauce on the grill while people are waiting). If you get enough char from the grill, some people might even say they taste good.
It helps if you think of it as a completely different style of rib. City-style vs. country-style, if you will.
Re: sous-vide ribs, I had an appetizer of baby back riblets that had been cooked sous vide until fall of the bone tender and then finished with an asian style glaze under a salamander. They were awesome. As tender as all get out, but not mushy at all. I'll definitely give it a shot some day.