I can think of a few differences between the American and British political systems that partly account for the difference.

First, there's our arcane election system. It's almost inevitable that the losing side will feel that it's been cheated somehow. In presidential elections, our electoral college makes it possible for one candidate to win the popular vote and still lose the election.

(In Britain, it's also possible for one party to win a majority of seats in Parliament without getting a majority of votes nationwide, but Britons don't seem particularly concerned about this.)

The fact that every state makes its own election laws makes us all suspicious that sleazy practices in another state will affect us all. (In Britain, the fact that election procedures are uniform apparently gives everyone confidence that everything's working right.)

And since there is no national supervision of election procedures, practices in some areas CAN be sleazy. (But most people seem to support the system in their own state.)

Our elections are held more frequently—every two years for congress, every 4 for president—and our candidates can spend an unlimited amount of money over an unlimited span of time—which means we are in an almost perpetual state of fundraising and campaigning. Lobbying groups and "swift-boater" groups can also spend an unlimited amount trying to influence elections, politicians, or public opinion.

Legislation often gets hung up on procedural matters. Bills can pass one house but not the other, or they can pass both houses and then be vetoed by the president. Or they can be enacted into law and then be declared unconstitutional by the Supreme Court. Whichever side loses is bound to cry "foul!"

The British system seems simpler. The House of Commons seems to be the only house that matters (I don't really understand what the House of Lords does nowadays.) and whichever party is in the majority seems to be able to do whatever it wants, with no constraints except their own consciences and whatever regard they have for public opinion. The losing side, the opposition, seems to accept its position more graciously than in the US.

In other words, in the US, people just don't seem to have confidence in the fairness of the system. There never seems to be a "clean" win and loss—none that the losing side ever accepts without protest, anyway. They keep saying and thinking: We should have won—we would have won if only the election had been run fairly—if only the other side hadn't lied and cheated—if only the media had let us tell our side of the story properly—if only they hadn't "bought" the election—if only they hadn't pulled that sneaky procedural trick—if only the public knew the truth about Obama's birth certificate—if only they had interpreted the constitution properly, and so on.