Afghanistan Election? What Election? Its BS!?

Can anybody explain why in a runoff election to determine who should be President, when the No.2 candidate decides not to re-run, the No.3 Candidate doesn't automatically take his place? This seems to be a Karzai clean sweep irregardless of the mes of allegations of corruption and vote rigging, some of which were proven thereby creating the runoff situation in the first place. I see that the USA were first to congratulate Karzai on his win. Is it a case of the USA supporting Karzai as a puppet? Will this situation alienate the opposition leaders' supporters, (about half the population), thereby creating an atmosphere likely to plunge the country into civil war? Surely the Taliban are the big winners here. President Obama can send 40,000 more troops, he can send 100,000 more troops but if the US is embroiled in a civil war situation and a fight with the Taliban within the country at the same time, he better send a load of body bags with the troops so they can come home again. Remember the 5 way civil war in Lebanon?