I thought an interesting point raised at yesterdays Neolithic conference was that the whole point of moving a stone may have been to get as many people involved as possible, not to move it as efficiently as possible.
In otherwords, there are societies to this day that build stone circles, they do it by dragging stones.
It may be that the size of the stone erected was a testimony to the numbers of people involved - respecting the monument. It may also be that innovations that make stone shifting easier were frowned upon - seen as cheating.