[sanderjd]

Ha, except, to go full circle, then if you're using that legal definition of a "gift" requiring a transfer of ownership, it's clear that open source software is not actually a gift, because there is no transfer of ownership.

You can't have it both ways! If it's a "gift" in the colloquial sense of something freely given, then it breaks social convention to claw it back, but it is not illegal. If you want to use the legal definition of a "gift" - ie. for tax purposes, implying a transfer of ownership - then contributions to open source software are not at all a "gift" in that sense.