I was told by my great uncle that this was intentional, as the powers-that-be thought it would be better to match the enemy's physical proportions. My great uncle, small in stature, was in the Pacific theater. My grandfather, taller, was in Europe.
Edited for a typo.
Absolutely not. I mean no disrespect to your great uncle, but it's so far out there that I really don't know how to disprove it, or what to cite to do so. Certain divisions were picked for assignment to the Pacific or Europe, usually while they were in training, or after they had completed training. A division is ~14,000 men, of varying heights and sizes, and they took at least six months to train up, assuming the division's personnel weren't raided for use as replacements, in which case the training process started all over again. They certainly didn't pull guys out of one division and send them to another for the sole reason of height.
Mansoor, Peter. The GI Offensive in Europe.