Once Hillary gets back on her feet, I'm sure that Rudy will as well.
The difference is that Clinton is the kind of person who wins the Democratic nomination, moderate on economic and military issues (to suggest that she's right on those issues is hysteria to the extreme) and left of social issues. Giuliani was never, ever a good fit for the Rep primary/caucus voters. His numbers were inflated by his name recognition and lack of decent alternatives. He knew that, and hoped that he could get an early win, or that there would be a massive squabble in the early states allowing him to coast in and steamroll on Feb 5, after a big FL win. Well... his strategy is screwed now.