Why is Barack Obama the only candidate whose campaign has a Facebook application?

Facebook has come under scrutiny for its alleged favoritism toward Obama, and some have charged that "Barack Obama's campaign has received an unfair upper hand from the online social networking site" in the form of insider pre-launch access to the Facebook Platform.

And not only that, but Facebook may have violated campaign finance rules in helping the candidate out. While their story is a bit murky, with neither Facebook nor Obama's campaign giving any firm answers, it is bolstered by an eyebrow-raising connection -- Chris Hughes, one of Facebook's founders, now works for the Obama campaign.

A simple search of Facebook apps shows that of frontrunners Clinton, Obama, Giuliani, Thompson, Romney, Bloomberg, McCain, and Edwards, only the Obama campaign has an official app (in addition to unofficial ones created by supporters). Either something very fishy is going on, or Clinton, et al have all just stopped caring about getting more votes.