There are also other differences such as error correcting memory in pro gpus, different clocks, etc. Some units that are not essential for gaming performance have been fused off in gaming gpus so that the chips can run faster and hotter.
It's funny how you never hear anyone complain about the fact that Intel's i3, i5 and i7 models are almost the same chip but there's a huge price (and perf) difference. Intel's latest product line has 22 chips of the same design, and they definitely don't have 22 semiconductor production lines.
> I wasn't aware that there was a difference at all. Haven't there been cases of changing a single resistor to switch the card's mode?
This was debunked in an earlier HN discussion, all the resistor hack does is spoof the PCI vendor:device identifier. The fused off parts won't come back up. It won't turn a gaming gpu into a pro gpu, it only triggers a bug in the driver that allows multiple displays (what a silly limitation).