I should also mention that there is another remedy to that concern (which I don't necessarily agree is that big of one) is another cultural component of the OSS world: forking. If the party you assigned your copyright to (and remember this would almost always be to a project not an individual), you have the option to carry on (or lobby for other developers to carry on) the project from that point under the GPL, one of whose main points is to guarantee your right to do that. Given the way the community would tend to react to such an attempt, a forked project would almost certainly end up being the new de facto standard.