Originally Posted by Sean Setters
It might also have to do with the design of the 24-70 f/2.8, which by many accounts is a stellar lens (I haven't had the opportunity to use one in the field yet). You can't just take an existing lens and plop in an image stabilizer...it requires additional lens elements and the circuitry takes up space. Adding IS to the 24-70 f/2.8 could quite easily have detremental effects on the image quality.