I know some biomechanics researchers at my uni use EMG as one of their standard tools. Always wanted to play around with it a bit...
As for Bret's work, while I agree that he did not perform a strict scientific study and given the tiny scale and, most likely, less than strict setup, the errors are probably quite significant, it still seems like something worth thinking about. I'm not obviously suggesting that everyone suddenly starts running EMG tests to figure out their best exercises (especially since factors other than activation would be meaningful), but it would be interesting to see the results of a proper study, ideally performed on multiple populations, for example with different body proportions and training histories.
I would imagine most (if not all) really big guys figure all this out by themselves, simply by trying exercises until they find the ones that work for them. Just one of the reasons why no two pros train exactly alike. No reason not to compare those "in the trenches" results to relevant scientific work.
On the other hand I am a big geek and I get almost as much pleasure from reading about all this as I get from figuring out how to do all this "in the field".