Any ideas what Google's criteria are for displaying Common Words?

Of 33 sites that I checked in Google's Webmaster Tools, only 14 show a Common Words report in the Page Analysis section.

I don't yet see a pattern in the two sites not displaying the info - for example, site age, complex URLs, presence of Google sitemap, etc.

* Common Words is a list of frequently appearing words Googlebot has found on your site, as well as in external links to your site. It shows how the Google crawler "sees" your site from a raw text perspective.

Dave at PrairieWeb