Best part being, its literally fucking impossible to steer. Take off the four little cart wheels, cut the bottom frame at the very bottom and put a small bike tire there. Then you would actually have something that functions, instead of taking an "action shot" on a straight away when he could never make a turn in that cart-mobile.
It would be a bitch if the store took back the cart while he was there, and left him with a bike with no front wheel. They spend a lot on carts, like $150-200 each, and take it pretty seriously. It seems like he would be able to steer his cart, just not very well.
If you look at his blog, he just flipped the carts wheels, the rigid wheels are in the back and the "Movable" wheels are in the front. If all of the wheels could move you may be right but I can't see how you would be able to steer at all. Just imagine your big having two wheels in front that can't move, it would be pretty hard to move if you could at all.