Perhaps I should have been more specific. I was referring in that sentence to Contributor License Agreements (CLAs), specifically the most egregious ones, such as Canonical's CLA that not only transfers your copyright to Canonical but grants them the right to relicense your work under any license they wish, even proprietary.

If I'm going to give something I produced away under a permissive license, I'd rather not be harassed to sign an actual, physical contract with some company as well, let alone one that places additional obligations on me while offering nothing in return.