One major difference:
In these places, IIRC, the Prime Minister (the chief executive-equivalent) is selected by the Parliament; he serves at their pleasure until the next vote of "no confidence" or until the next scheduled election, which ever comes first.
In the US, the Chief Executive would be chosen directly by the electorate, thereby limiting the effect of any nth-party candidates on the selection process. A run-off election will still result in a direct election of the Chief Executive; any nth-party candidates forming Parliamentary-style "coalitions" will mean squat in the "forming of the government"; all it could possibly do is make passing legislation more difficult (which may or may not be a good thing). Note that the concept of a "no confidence" vote will still not exist in the Constitution.
