Just to save my time typing, I would love to quote @Nargil . I agree with him 100% ... Keyword density is one of the most important On page optimization factors nowdays. Screw it up and you are gone. The problem you took it from the wrong angle. You don't need keyword in content to rank using two of the most authoritative websites on the web as example. Actually, it matters cuz it's the easiest and fastest way to get over-optimization penalty. This is actually what 85% of SEO'rs problem. For me, if my page doesn't appear in top 50 for medium to competitive keywords, or to 30 for weak to med competition keywords, I know there is something wrong with my article. Yet, many people are happy with their page appearing in +100 position and go buying all types of links to rank! They are under over-optimization penalty. So, keyword density matters, and matter A LOT, more than heading, and more than anchors and more a lot of other things. Screw it, and you just made things 10 times harder.