Well, this is just guessing, having read nothing specific on this
particular question, but I suspect the answer is more mathematics
than anything else. There are only 3 polygon shapes which 'fit'
together - triangles, squares (or rectangles) and hexagons.
And, only hexagons allow the shapes to be varied in a 'non-regular'
manner.
But, just a guess. :-)
Cheers,
-- Bill Shatzer - bshatzer@orednet.org -or- aw177@Freenet.Carleton.ca -