Self interest as well. Lots of companies want you to sign additional agreements on the way out (don't trash the computers, don't bad-mouth the company, etc.) and you have no reason to sign these if they don't give you something in return.
just what I was going to say. it his blog he mentioned they were faxing out some 'agreement' for him to sign. My immediate reaction was 'why the fuck would he sign anything?'.