Why does the American political system work?

Simply because America is rich.

The reasons why america is so rich and powerful today isnt mainly due to their system of government, which is really the bastard child of the westminster tradition with more powers for the executive. The reasons why America is so succesful today is the length, breadth and wealth of their land, the two world wars; which they profited from in a big way if you look at in the light of how much europe and the rest of the world lost, the idealology of how america came about; basically America was founded, and in later years developed, by group's of people looking for wealth, and that coupled with a dislike of authority, created an 'everyman for himself' society with those with the best buisness sense normally coming out on top.

The reason why countries have failed in adopting the Westminster system as America did, is normally beacause; of the traditions already in place in that country, the way in which the system was founded and the mentality of the people; even though America would argue otherwise, democracy isnt the answer for all peoples of the world. An example of the westminsterr system working is my country, Australia, however the reason why we arent as prosperous as the Americans are; our country was settled by europeans with a different agenda and at a later date, circustances havent gone in our favour the way it has the Americans and mainly because of the fact that most of Australia is very barren and dosent have the riches of mainland America.   

hehe

well i suppose it'd be kind of hard to predict what kind of economy we'd have if we had 10 times our population because its not v likely to happen within the very forseable future. Too much of our land is barren really.