and for yet another variation: Mayburgh henge, the banks are made of stones, with no ditch on rising land and only a mere spit away is a regular earthen one.

i like to think of them in terms of the plans of christian churches/cathedrals, in that although all those buildings follow a similar cruciform layout and have the same function there is much variation in elavations. not just in period style, but that some have porches, narthexes, towers, steeples, lady chapels, etc, whereas others don't, but essentially they do the same job.