There are a couple of reasons for this. 1. The key phrase is long tail. A more heavily trafficked key phrase may or may not score the top listing depending on keyword difficulty and the competitor authority. 2. Google assigns serious weight to domain names and the closer you are to an EXACT match for whatever key phrase you are pursuing, the better off you are. 3. It is very possible for an authority site to out rank a site with the exact key phrase match. Therefore content is still king. This is however one of the more compelling reasons as to why I own over 4000 domains, now if only I had the time to develop them!!!