Why is it that so many people want an EF 24-70mm lens with IS ?
There's been reports of QC issues with the current EF 24-70mm (focusing problems, etc.).
Also, an H-IS version of this mid-range zoom would give you more control in low-light situations.
Two more reasons:
1-If it was H-IS, it would be even better for video, and video seems to be big for Canon (and growing for that matter).
2-Some people like to use that nice sharp lens stopped down sometimes (say for landscape), but they don't always have a tripod (happens to me all the time); IS could be really handy in a situation like that. It is basically taking one of the most used lenses, and giving it one more tool.
But the 24-70 is a portrait lens, canon wants pros to invest in other gear. And if you really want to stop down for landscapes, you will use a tripod, or otherwise use flash. Get the 24-70 f4 is if the is, and stopped down sharpness is important. This lens and the 85mm 1.2 are some of the lenses that I wished they didn't put on aperture blades, if you need to stop down, there is an alternative.