What's so special about two years? Is that how long before the yellow cake arrives?
2 years = June 2008 = US Presidential Election
just a theory....
Besides, they probably want to set a date for the same reason we don't want one and they knew we would have given them the finger if they had tried to say 1 year. That tells them how long they could bide their time to try and come back and seize power since they can't win it outright.