ive been taking a look at lenses lately, and noticed that the high end and the more focal length is nvolved, the higher the chance of IS being included. For example, the following lenses don't list IS:

EF 70-200 F4L USM
EF 70-200 F2.8L USM
EF 200 F2.8L USM
EF 400 F5.6L USM
EF 24-70 F2.8L USM

Not looking at one of the lenses in particular, just unsure why IS isn't offered with these lenses. I would have thought they would need it due to the focal length.

Anyone know why this is?