I'm really glad that you are not having problems with your G5. Seriously. But, how is what you described not your workflow?
Regardless (semantics aside), video editing tends to be more CPU intensive and batch photo editing tends to be more GPU intensive. This is why I am NOT complaining about my video editing. I just want the option to put a better GPU in my Mac Pro. This is a MUST for me. How many 1st Gen Mac Pro owners got tired of waiting and just said "**** it," eBayed their old Mac Pro, and bought a new one in order to solve this problem? This is not a road I want to go down.
I guess some people buy a new car every year, and some people (like me) like to buy a new car and then enjoy it for 2-3 years before trading it in.
I would bet
most people know next to nothing about 64-bit EFI implementations. You don't know what I do or what my degrees are in. Don't make assumptions of what people know or don't know.

This problem is not a question of difficulty or technical challenges. The 1st Gen Mac Pros are fully capable of supporting the 8800GT, given the right supporting drivers/firmware. Apple obviously invested the software engineers' man-hours into developing this for the Early '08 Mac Pros and
didn't do the same for the previous generation Mac Pros. Why? Well as you say we have "no idea what decisions were made." But it doesn't take a software engineer to figure out that it's all about forcing the new Mac Pros down the throats of 1st Gen owners. And from some of the comments I've seen on this thread, it's working.