Entry pages as indication of online visibility

is this a fair assumption/assessment?

[fom2001uk]

I'm looking at the top entry pages for a site with hundreds of pages. I'm working on the assumption that most visitors entering a site on a page other than the homepage, would have come via a search engine. I accept that some may have been bookmarks or links from other sites, but that these would make up only a small percentage.

Therefore I'm looking at the activity levels for each page as a guide to how visible they are (ranked, optimised, etc)

Is this a fair assessment?

[ScottM]

I've been told to treat every page as an 'entry' page, and to act accordingly.

More often than not, if I see a page performing well for a term I haven't optimized for, that page gets a little more of that term. (One never knows what awaits at the top of the SE's for a term you didn't even think of!)