I quickly put up a nintendo wii topsite last week and sorta forgot about it, and to my great surprised found it to be the 3rd result in google for the search term "wii topsites". Well, firstly, does this add value to my domain name? And secondly, (a bit off topic) is my high ranking search result only because my domain name if descriptive of my site's content? I'm a bit new to all of this, so go easy.
So you're saying that you just put a web site online and in about seven days it ranks number three on google? I would never sell that web site but to answer your first question yes. When a domain name contains keywords that match what they find on the site it assumes that the web site name is a good descriptor of the content.
It means not many people are searching for that phrase. You should consider targeting some slightly more searched for keywords.