Your point still stands, but these guys are tinkerers. Upgrading a machine that wasn't strictly designed to be upgraded is half the fun. The more difficult to job, the more rewarding it is when it comes together.
I understand where they're coming from. I also have one of these machines and I intend to build it up somewhat. I keep spare Logic Boards, Graphics Cards (6770M and 6970M), Power Supplies and even an LCD for it. I have a faster processor waiting to be installed, and the machine has already had an OWC thermal sensor kit installed earlier this year. It's amazing the spares you can salvage from machines that took a fall or were damaged beyond economical repair in transit.
It isn't the easiest machine to work on but it is hands down my favourite. I take apart newer iMacs every day and although this needs a glass cleaning with every disassembly, I still prefer it to the cut-and-restick nature of the newer machines when it comes time to make some changes internally.
Watching this thread closely, if we do succeed in making another GPU work in this machine I'll be tempted to make the switch as well.
