Why make your own? Because it will taste better than any supermarket chunky or creamy crap, and it's not that hard to do yourself! Or at least not that hard for an Alton Brown recipe.
Just fry peanuts with peanut oil in a wok, let them cool down and then throw them in a food processor. He has his own instructions to add some crunch to it, which, let's face it, is the only way to go with peanut butter.