Must admit having IS on those very short lenses is a bit of a baffler - even handholding you won't notice much shifting of the frame unless you have a very bad case of handshake. I can only assume that the optical cost of adding them (ie optical performance) was marginal to nothing and so they put it in to have as a feature over competitors; having companies like sony pushing in who like in-body IS might well push Canon (maybe Nikon) into adding more IS to lenses, even if its not needed so that they can also boast a high amount of IS in their lens range.
Not having it in the zoom makes sense though, the current zoom is a workhorse for many and if they've boosted optical performance anything like what they did with the 70-200mm MII then that new zoom will be a near prime sharp lens through its range. Droppings its weight will also attract some since "the brick" is a nickname the current one has earned .
