aristotle - 12:44 am on Apr 16, 2012 (gmt 0)
In my opinion, on a well-designed site the pages will tend to support each other. For example, even if a particular page doesn't get much direct traffic from Google, it still may be helping the rankings and traffic of some of the other pages.
I believe that the Google algorithm looks at the whole website for determining which keywords and/or key phrases to associate with it. I also think the algorithm includes both indexed pages and non-indexed pages in its overall evaluation, including pages that have a noindex tag in the header.