There's also the fact that the government would not be cancelling allnof their contracts with these companies, so they'd still have some defense and non-defense contracts. There are few things more dangerous than having to rely on people you've just screwed over.
And these companies don't just make military equipment. Boeing and EADS most definitely make civilian equipment, including aircraft that almost all of us have flown in, most likely.
So if you're the President, flying around in the Boeing-built Air Force 1, which requires spare parts and maintenance from Boeing, you're not gonna screw Boeing over by refusing to pay your part of a contract.
Oh, and there are international repercussions as well: EADS is partly owned by several European governments. Now would be an exceptionally bad time for a mutually suicidal trade war.
That doesn't mean that contracts shouldn't be cancelled if need be, just that you really need to honor those contractual obligations because you need those contractors for other things.
He pulled a Captain Ahab and Jaharpwn'ed her. - Trout