I'm too tired and occupied with other things to offer an analysis, but I think it has a lot to due with the elements of Federalism built into our Constitution. The significance of controlling the Presidency has been demonstrated in the last two years, but the importance of the fact that the President is elected, essentially, by the States, and by the people only indirectly, was demontrated to us all in the 2000 election.When you're rested, give me a ping on this. I understand from you that federalism demands the two-party structure in that further divisions of power would be counter-productive in the two-tiered Congress and to pull weight on presidential elections. But this is not the case in other countries, even those that mimic the U.S. model.
I certainly agree that the parliamentary system fosters stupid factionalism. I'm not sure that this leads to the opposite, given the federalist/ representative system. But perhaps.
Either way, it's a blessing.
Other countries, even those " modeled " on our system, don't really have our sytem. That's the simplified answer.