This doesn't make any sense. NATO officials announced today that registration for the Afghan national elections is complete. According to the Associated Press report, 15.6-million people have been registered to vote, up from the 12.6 registered for the 2005 vote.
If voter registration is finished in mid-March, it's hard to understand why the general elections had to be postponed from May (the date under the Afghan constitution) to August (the date picked by the electoral commission).
It does sound like the fix is in. There has been speculation that the three-month delay is intended to allow potential rivals to Hamid Karzai to come forward and campaign.