the problem with valuing domains based on their search engine optimzation potential is that is relies on additional activity and does not offer any inherent qualities to the domain itself.
You can create a keyword laden domain name (or names) very easily even for top terms. e.g. casino-video-poker-roulette.com
Domain values have to rely on inherent and intrinsic qualities like descriptiveness, desirability, guessability, ease of memorability etc moreso than what *could* be done with it - otherwise every domain would have to be valued based on what would happen if the words best seo met the worlds best web design met the worlds best marketing.