Do this: post a video of your 'natural gait' walking please. I want to see how it compares to the video below. It is my theory that in order for you to land similar or exactly how the runner below is landing you have to take much shorter steps to ensure that your hips align with your feet. This is easy to do when running since you're propelling, or pushing yourself off, then "catching' yourself at the right time. When walking you lack this momentum, not to mention the amount pressure is less, so it's perfectly safe to land heel-first.
(I'm incredibly bored, thus elaborating way more than I should...)
Also, you may be under the impression that I'm pointing my toes up and taking extra measures to put all my weight on my heel, because you keep saying how I'm going to drive a nail into it and my walking days will be over, but that's not the case. My midfoot makes contact with the floor very soon after my heel. In the event that some random object is threatening the health of my heel it can only do so for a fraction of a second before the rest of my foot lands.
If I had to walk like the runner above runs I'd never get anywhere. I can't see any other way to mid-foot strike than to walk super slow or lean forward ala chi-running, even then...