Interestingly enough, if you look at the history of the presidency it has only been in the last 50 years or so that a VP was presumed to keep the same spot in the reelection bid.
Cheney is a great VP, with all the threats out their against the President we can't afford to have some PC choice for VP, we need someone who projects strong leadership skills.
It has been going on ever since Cheney was named by Bush as his running mate in 2000.
No doubt we'll be hearing the same thing until January 2009, when Cheney finally gets out of Cheney's house!