Because everything on the Internet is True.

(or people have no peer review and can write any hair-brained things they want, and some other people will believe the fabrications. So much for freedom of information, when it's freedom for nuts to have delusions, and share them)
In Henrys Historia Anglorum, written about 1130, Stonehenge is the second of the four wonders of England.So much of no early records and it was built in the 40s?
Plus if one believes the excavations and scientific research, beaker people, carbon dating of remains, bones, and all the rest, the website you linked to is pure Hogwash. Avebury, Old Sarum, Amesbury, and a long list of others. Although I will confess, Stonehenge is not as mysterious or amazing as the books want you to believe. Not in the time of the Druids, not Wicca, but the eccentric people will dress up and go there on the Solstice anyway. They are selling myths, pseudoscience, and books.
It's a very special ancient place and new discoveries are made on further investigation. It's interesting. But not some convergence of lay lines, built not by ancient astronauts, or not even an amazing calculator.
Last of all, it's not a Henge at all. The ditch is on the wrong side of the embankment.
I have found this amazing:
http://bit.ly/14kJ2SD