It's probably marketing. For that amount of money you either buy a fast f2.8 lens without IS or a "slow" f4 lens with IS. This way they can sell two types of lenses. The production cost of the f4 lenses are mostly cheaper so if they would apply an IS system to the 24-70 they would cut their own fingers pretty much, because the demand on the 24-105 F4L would drop like crazy.


If you follow the Canon rumors and demands of photographers a little bit, you'll see that a 24-70 L with IS is probably the most "hoped for" lens there is. It's rumored to be announced ever since I started photographing so at least 2,5 years or so []


I doubt it will come and if it will, it will be in a different budget probably[A]