Craig Resigns, Vitter Stays in the Senate, What Gives?

Larry Craig (R-ID) pleads guilty of lewd conduct in a bathroom stall and resigns in disgrace. David Vitter (R-LA) is outed in a prostitution ring in DC and cheating on his wife and gets cheered by his Republican colleagues in the Senate when he returned to the Senate.

So what's the difference between these two?

The most obvious one is that Craig was attempting to solicit gay sex. However, the main reason Craig resigned and Vitter is still in the Senate is based on politics.

Larry Craig resigned because he is from a red state that has a Republican Governor. Now the Republican Governor gets to appoint his replacement. David Vitter is from a state with a Democratic Governor. If Vitter would have resigned, the Democratic Governor would then most likely appoint a Democrat to serve out Vitter's term.