Scott,
Can not speak for everyone else, but I have the gas forward on my Broadbill to help maximize use of space (and in this case, not have to fight with the gas tank to hunt the boat low blind), as well as push the center of gravity forward to help with some porpoise issues I was having. Started out the same way on my BBII for the same reasons, but have since concluded that boat handles rough water better with the gas in the back. The BBII is roomy enough that having the gas tank in the rear does not cause too much clutter, even when hunting 2 people.
-Bill