>What are the odds of a belief system, both spiritual and architectural, being very similar >throughout Britain and Ireland during the Neolithic and Bronze Ages?
I get your meaning TE, and I don't think that spiritual and practical considerations need to be mutually exclusive things. But it's easier to notice the similarities than the differences, and tempting to gloss over the latter in favour of bigging-up the former.
Mind you, I've got a thing about cup-marks, and they're virtually identical all over the globe, so I do reckon there's something in the idea that there was some kind of meta-cultural template waaaaay back whenever. Paleolithically even, whocansay?