I'm aware that corn plays a huge part of North American diet (less so elsewhere since corn-fed beef isn't nearly as common), but I've never heard it said about potatoes..and while you mention it, you only provide links about corn.
Don't mean to be flippant, but it kinda sounds like you lumped potatoes in with corn for the sake of it.
And a lot of US corn and soy is GM. I'm guessing the majority of which is animal feed.
See Jeremy Rifkin's: Beef, if you want to read up on a fascinating piece of North American history. Nice fatty corn fed beef was (and probably still is) highly prized.
Don't mean to be flippant, but it kinda sounds like you lumped potatoes in with corn for the sake of it.