I do not claim knowledge beyond my own little slice of heaven.
However, if you think polling occurs anywhere beyond selected urban sights, you are wrong. Afghanistan is a rural country, and pollsters are not hanging out in khaki Afghan or Shamulzai.
The election results don't suprise me, look at the voter %s. Karzai is many things, an inept politician is not one of them. He manuevered himself very well to ensure that he won the election. Too clever by half. He had no need to cheat, and very well may have had no hand in the voter fraud.

That he was elected was not an endorsement of karzai, it was a resignation by the people of afghanistan that there was nothing they could do. When he shelved Sherzai (his only legitimate rival for power) his success was assured.

Karzai knows how to rule Afghanistan in a tradition sense. Its the traditional sense of ruling afghanistan that brought us where we are today. The best traditions of Afghan society (decentralized limited government) are being discarded for the more standard kleptocracy of every other failed unstable state. And we are empowering it.
Again, we can legitemately state "mission accomplished" and go home leaving Karzai to fend for himself. But as long as we are propping up his state with investments of blood and treasure, he should dance to our tune.