Detroit blackmail?

Can anyone explain why GM and Chrysler say they'll need $100 billion and $25 billion in financing respectively if they have to file bankruptcy, but far far less if they stay out under the latest hat-in-hand plans they've brought to DC? The enormous difference in magnitudes feels like it's part of Detroit's rhetorical blackmail to get the fix it wants (i.e. not bankruptcy), but maybe I'm missing something.