Not necessarily. Mack has now closed with Nelson. The Ds stand a very good chance of getting slammed in the senate if they don't regain some footing. McCaskill may lose in MO (it was a gimme a month ago), Heller is up 10 in NV (that race was almost tied a month ago), Mandell is up in the latest OH poll (that was a D seat a month ago). So perhaps the DNC thinks Obama needs to be there to help turnout for Nelson.
I don't know anyone, including the usually unreliable pollsters, who think Obama is still alive in FL, NC, or even VA.