Navigation on the Bottom
What device do you visit websites on the most? Desktop or smartphone? I'm no psychic but my guess is your smartphone. I base that on the fact that a rather large percentage of web traffic is done on mobile devices. So now that we've established that you visit websites mostly on your phone lets note the location of your hand. Do you hold your phone up at the top? or are you holding it towards the bottom? I shall take another guess and say towards the bottom.
So you're on a website on your phone and you're holding your phone in your dominant hand. If you have anything bigger than an iPhone 4s, you're going to have to do some reaching if you want to get to the navigation bar. Or maybe you have to use your other hand to press. Is that how it should be? I say no.
Our world is filled with web designers and user interface designers. Yet navigation is still predominantly placed at the top of the screen. Your argument that Apple has reachability and such is valid. However, yeah but still. Navigation should be on the bottom for mobile devices. where your thumbs are.