Martine van Bijlert, co-director of the Afghanistan Analysts Network, hears rumors:
The whole prospect of a possible second round is seen by many Afghans not so much as the outcome of an investigative statistical process, but rather as a means to force a preferred outcome -- whatever that may be. And so it seems that the Karzai camp is calling Abdullah’s (and the international community's) bluff. You want a second round, you can have one -- very much in the same way as Karzai caught the opposition off guard earlier this spring when he suddenly gave them what they wanted: an election date within the Constitutionally prescribed deadline (but logistically impossible and politically impractical).
The whole post is well worth reading.