Contrary to the prevailing narrative, Real Clear Politics' Tom Bevan argues that there are five reasons Hillary won't run for president in 2016 (these are all direct quotes from Bevan):
1. "She's just not that good at campaigning."
2. "The “fire in the belly question."
3. "It ain’t gonna be a coronation."
4. "Obama is leaving a mess."
5. "The country wants real change."
As noted, this is a really weak argument. There is only one true factor governing whether Hillary will run, get the nomination in a cakewalk, and (baring serious economic slowdown or the similar national crisis) have about even odds to win in November: At her age, does she want to go through all that and serve potentially 8 years at the toughest job in the world?
(Before anyone accuses me of sexism for referencing her age, I'd say the same about any male candidate who'd be pushing 70 at the 2016 election. I'd say the same about Biden if I thought he was a viable candidate).