We've always done it so it must be right, has to be. I understand the aspects behind insulin sensitvity, I understand that post workout carbs plus protein will lead to a higher anabolic response.
Let me ask you, there's typically three goals
1) Lose Fat
2) Build Muscle
3) Lose body fat while trying to increase lean muscle
The majority of the people are 1 and 3. If you were just going for shear muscle size, then go ahead and have your carbs post workout. If we are like the rest of the people we need to minimize our insulin response.
It isn't right or wrong but try it, if you train 4 days a week, make 3 post workout shakes carb less. It can't hurt your cause.