That's a very interesting theory, but I run 40 miles a month, and I have to hope my heart is MUCH better at recovering than a fat person's.  If being fat and running daily were the same, well shit, I don't want to live in that world.  Everything you said is food for thought though, and hell parts of it may be what is going on with this but I don't think you've got the whole thing here in your post.  There's a lot more to it.