Funny you say that, because a friend and I were having this discussion a while back about how spiking insulin "sky high" and on a regular basis, regardless of it being down peri-workout, is still possibly bad physiologically, with the potential to bring even healthy people into the category of pre-diabetic.
(hope I articulated that properly; just got home from some bar hoppin)
Another friend of mine would take something with high GI carbs and protein as a PWO shake, and he would consistently feel shakey for about 30 min after ingesting the PWO shake. He wasn't even overweight or pre-diabetic (if I recall).
And if you think about it, it's not like most natural foods allow us to spike our insulin that high, plus we tend to eat a mix of macros (and ideally with fiber) that lowers the total GI of the meal; hence, a PWO shake can raise insulin to artificially high levels.
At least, that is my logic. Glad to hear someone else thinks along the same lines.