Astonishingly, I hear there exist problems with the functioning of communities that can be solved by means *other* than duplicating the American constitution in microcosm. Heretical thoughts, I know, but there you are.
American's do seem to have a habit of thinking that clear separation of powers is a necessary part of any fair government... the UK manages fine without any such system. (For example, the Attorney General is a cabinet minister (ie. lawmaker) with the power over criminal prosecutions (judicial).) I think the main reason the US needs the separation of power is because of the enormous power held by individuals. In the UK, there is almost always at least some degree of parliamentary oversight. I think Wikipedia is closer to the UK system - no individual can just do whatever they like, they always need the support of the community.