Don't you guys think it's an approach that Canon usually gets its f/2.8 without IS (e.g 16-25/2.8, 24-70/2.8, 70-200/2.8 ) out the door first? That can showcase what they can achieve.
Then sometime later they release their f/4 IS variants (e.g. 16-35/4 IS, 24-70/4 IS, 70-200/4 IS) to suit...