I have read that, too. However, that is how the thing has looked to me for a long time. As a piece of sculpture it appears to have fallen into inexpert hands. They didn't even blend the new head and neck into the old body, size disparity aside.
Yea, could be, but then who were the experts that built all the other things around there. Like you said, the splendor of the (new) Cheops pyramids. I find it hard to believe that something of that magnitude and public display would have been left to an inexperienced sculpture. And considering all the stone work going on during those times, it's not like it was a lost art or something.
But I agree other forces/damage could have required the reshaping of the head.