I can totally understand Canonâ€™s take on no IS for the 24-70 II, though this is a rumor at this point.
The primary reason could well be because such a lens, with IS in the general zoom range has the potential to cut into a number of their revenue lines â€¦
The current 24-70L f/2.8 targets a specific consumer rung, who are willing to pay a good amount but not the bank. They are willing to choose a contracted focal range but a faster f/2.8 lens provided the pricing is not way too high. We are not talking about the well-heeled pros with all the L-primes in this range and beyond. The â€œdifferentialâ€ contender with longer focal range would be 24-105L, a peg down in the marketing line (I am not inviting a flame war here on merits of these two lenses, just where they fall in the Canon product line and pricing) which continues to be a good seller for Canon.
If pricing on 24-70 version II is low enough to tread this fine line, with the faster f/2.8,and IS, it could cut severely into the 24-105L f/4 line even with the longer focal range enticement. Hell, it may even cut into the sales of some of the much older non-L primes which are still on sale from Canon. No one wants to cut their own legs shorter.
Marketing and where to put a high-quality fast IS zoom in the price/consumer range may be the deciding factor here. They may do a 70-200 f/4 trick on us and release an IS and non-IS version, but thatâ€™s probably too hopeful.
Cynical, but a smart Canon &@#@@!!!