I don't know, for those with only 35mm gear (or maybe even 6x4.5) I see it. I too shoot 4x5 and don't see much appeal in a beast just as big and heavy. I DO love medium format, which for me is a Yashica Mat 124, but that is a small, even tiny compared to the RB, easily hand held camera, and I find I carry and use it where I would have carried and used 35mm before. It replaces a smaller camera as my walk around easily hand held camera. If I have time to use a tripod and really think about what I'm doing, I use my Technika III.
Maybe if I tried one I'd get it. I have really loved the Yashica though and have been eyeing either another one, so I can carry two types of film, maybe a Rollei, or a 6x4.5 system, particularly the Mamiya for the 80mm f/1.9. But I don't yet see the appeal of a medium format camera as big and heavy as my 4x5.