Hillary could skip the 2004 primaries knowing that she would still be well-known in 2008. Turns out she miscalculated--2004 might have been her best chance of winning, but she didn't foresee the Obama phenomenon when she had to decide on whether to contest the 2004 primaries.
Pawlenty and other wannabees don't have that luxury--if Pawlenty does nothing in 2012, by 2016 he'll be totally forgotten.