Oh, poor USA, its constitution is no longer the model for the world. Well, just mayhaps it could be that the heaps of scholarship about things like Proportional Representation and Asymmetrical Federalism and other alternative democratic institutions may have had an impact on what countries do.
Canadians will jump to take pride in the supposed popularity of their constitution, but most new democracies are not adopting British-style political systems. They are mostly developing rules that pick and choose from existing models. Lots of effort to avoid tyranny of the majority, which was a key part of the development of US institutions and a key aspect of British-style systems. Not going to see too much first-past-the-post stuff.
Oh, and even though the Canadians argue with me about it, the reality is that a province or the national parliament can decide to ignore rulings of the Supreme Court with a simple majority vote--due to the notwithstanding clause. Sure, it only applies to fundamental freedoms, legal rights and equality rights (not democratic rights, language rights or minority language education of citizens (sort of). That is, provinces and the national parliament can abridge fundamental freedoms but not language rights (well,e except for immigrants in Quebec, I guess). And only for five years (but renewable every five years).
Anyhow, the larger point remains--countries with relatively new sets of rules are learning from the past experiences of other countries but also building rules that benefit those already in power. Because, hey, making the rules is POLITICAL. In any case, the US system has pro's and con's, as do British-style parliaments as do the European institutions. Smart folks will try to figure out which circumstances outside their country match their situation and then choose those institutions that have the desired effects (stability vs. adaptability; minority protection vs. efficiency, whatever). And learning from the social science of this is not a bad way to go. This is one of the areas that has received much attention and will continue to do so. Just saying that the American rules are always best is just as silly as saying the Canadian rules rock! They may rock! But they may not work elsewhere. Unless you like a constitutional crisis every fifteen years.