Hmm... I wonder if that's the trick. 60 cubits is a varying measurement, so a few inches/feet here and there is good enough for some scholars! ;o)
Dan Cruickshank seemed quite sure the measurements (he did it in feet and converted that to cubits, rather than the other way around) were the same. Had his tape measure out and everything... And I think it's against the law to lie on telly.
As I say - I'd like to see the prog again (and maybe pay attention next time!) just to make sure...
That link Nigel posted - http://www.heritagecities.com/pdf/aerialofcircus&rc.jpg - is a fantastic example of the suggestion of sun and moon symbols, a-lá the masons...
Also interesting to note the height of Silbury being stated as such...
More research required by me, I think!
G x