Anybody that doesn't think IS is useful on a 24-70 is such a limited shooter I really don't understand your opinion. I can understand people not wanting or needing it for their style of shooting, but to deny it is necessary for some others needs and style is just crazy.
For a start, as has been pointed out, dragging the shutter would work much better to include some ambient that isn't too blurred, IS will help the ambient while the flash keeps your subject sharp. Secondly, more and more places are banning tripods and monopods, try shooting anywhere in India where you would want to use a tripod and armed police will stop you very quickly! But places like museums and cathedrals normally don't allow legged support.
I shoot a lot of travel photography, often I just don't have time to set up a tripod, like the first shot below, it was a stumbled upon situation at Ankor Wat that unfolded for three or four seconds 40 yards away, I ran to get the two shots I could before the scene changed, shot with 1Ds MkIII and a 24-70 @ f2.8 and 1/10 second, I would have preferred a steadier image but to print big was stuck with the iso, and before anybody says well newer cameras have better high iso, I know that, but that would just enable me to shoot even later, or darker, like the second image, iso 800 (I print big) f3.2 and 1/2 sec exposure, my subjects were not moving enough to cause me issues, I was at the limit of my ability to hold that focal length and shutter speed combination and that was only EV 1, my camera can work way darker than that, but until I get IS I can't.
I have no interest in a MkII 24-70 without IS, my MkI version is plenty sharp enough for the big prints I make, I would buy in an instant a 24-70 f2.8 IS. I would also buy a 16-35 f2.8 IS as well as a 14-24 f2.8 or f4, the former for travel the later for real estate. As, for me, the cost is offset I don't care too much what they end up retailing for just so long as they have better IQ and functionality.
Very well put!