This is true, but I once tried to design a spacefaring "Indian" culture andEDG said:Though just once (and getting very tangential) I'd like to see something based on Indian mythology ... there's a huge amount of great stuff to borrow from there, and it's scarcely been touched by western media.
had to give up because India has too many very different regional cultu-
res, and the plan to "combine" them into one single culture just did not
work - the result always turned out to be more of a caricature of India
than a plausible culture.

Right now I am working on a small (non-SF) campaign based upon the
Tibetan culture, as a single and comparatively uniform culture is much
easier to "translate" into a roleplaying game.