Best not to imagine because they're both sold way past the manufacturing cost and I'm not under the impression that nvidia puts all the money back into development.

At least not the development of GPUs.

The margins are irrelevant here. If Nvidia sold them for the exact cost of manufacturing, people would just scoop them up and re-sell them to the highest bidder. So in the case of 0% margin, some useless middle-man would get to profit.