Stonehenge is a trip and lot's of folks have spent lot's of time trying to figure it out! Well, as an archaeologist let me say--anything is possible! recent work there suggests that the whole site is even bigger and more complex that they thought it was. But me thinks what is important is that they did it-sometimes especially in the new world without either draft animals or the wheel!
Thanks for posting this. I saw something similar not long ago about Easter Island. Someone figured out that as long as the heads stayed upright they could walk them a great distance. if they fell that's where they stayed. Which explains the few heads laying about.