I was just kidding about global warming resulting in bigger bugs.
So much for humor.
What an old timer told me this year - not sure if it's accurate or not - but he said the size difference is a result of in-breeding w/domestic turkeys, and now our turkey "herd" is bigger than the original species were (he was referring to Eastern's down here in AL). He said, years ago, when he was killing the "original" Eastern species, a "good" bird was 18 lbs. max. Average was 14-16 lbs.
Again, don't know if there's any truth to this or not.