>>"one model is to have the exact same code with multiple licenses, one open, one closed."
>I don't understand. why bother with the later then ? what's the benefit ?
the benifit is that companies that are paranoid about GPL 'infection' no longer need to worry about it. MySQL's business was based on doing exactly this, selling the same code that was available under the GPL under a closed license for people who didn't want to comply with the GPL (or were afraid of what the GPL could require them to do, even if it didn't)
I agree that full copyright assignment is overkill for any of this. I'm not trying to claim that full copyright assignment is needed for anything.
however I am saying that there are reasonable ways to dual-license code, and that if an organization is going to do so, they will need some contributer agreement that gives them the right to do so with the code contributed from outsiders.
copyright assignment gives the company the ability to so this, but it's not the only way for this to happen