Have you considered that they may have a lot of links related specifically to that keyword? Sometimes we see keyword-laden domains ranking highly and assume that it is because of the domain, but it could easily be due to other factors.
My theory is this: Keyword-laden domains are an important ranking factor for only some sites. For other sites and categories it is not an important ranking factor.
Google has a lot of past history to work with for a given keyword or keyword category. I believe that ranking factors now vary considerably across the web for different keywords and site categories.
What holds true for one keyword likely does not apply to the next kewyord.