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.
Well, that makes perfect sense. All the more reason to be suspicious! ;p