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Checking some other sites, moderately linked but not highly competitive, I see that Teoma seems to pay more attention to text density than Google does.
No time right now to look into the more competitive areas. With most engines, what I've seen is that linking kicks in as competitiveness goes up. Below that level, on-page factors are still important... and even in very competitive areas where linking is a big factor, on-page elements are important in "guiding" the engines.