Everyone else is speculating so I will throw in my own two cents.
Bush has said that he does not need to pardon the people engaged in "enhanced techniques" etc, in our war on the noun, because "we do not engage in torture." Wouldn't that be funny if he actually believes that and really has not believed that a pardon was necessary! Cheney and friends of course know better and perhaps they felt they had to publicly acknowledge their role so that Bush would feel obligated to grant the pardon.
An Interesting aside to this is that Mukasey announced now (click on title to read) that by AG nominee Holder declaring "water boarding to be torture" many of the Bush war criminals are now at risk... so even though chief of the GTMO prosecutions "convening authority" Susan Crawford this week called the torture of one of the gitmo detainees by its real name "torture" these war criminals can now hide behind the fact that Holder has said water boarding is torture. Icing on the cake for them and now Bush will most likely be pressured to give the pardons (if he was not convinced that it was necessary)... And most likely he will use Holder as his excuse for entering the pardons (and conveniently ignoring Crawford's own statements?) ("My fellow American's we do not torture... but now this new upstart AG is suggesting that what we did was in fact torture... I just can't let our good people who were protecting us all be prosecuted for doing what we all know was right and necessary"... and blah blah blah....question is will he admit that he ordered the torture and then pardon himself....?
Just another theory to float out there on a cold and snowy Saturday morning.