Exclude Pages from Navigation Bar?

I have blurbs (e.g. about blog, or about author) on the start page of my thenme and the user can write and edit the blurbs by simply creating a page.

Now I want those blurbs to not show up in the navigation bar, not even for the admin.

For the past hour I’m going through all the files trying to find a function that may help me achieve this. I have a WooThemes theme where you can tick off the pages you don’t want in the navigation bar.

They’re using the standard wp_nav_menu() function to display the navi bar, and then they have their own show_page_menu() function, which they use to exclude pages as far as I can tell.

But I simply can not figure out what the actual cause is to exclude the pages, I can not figure out the system behind it so I can write my own function.

Does the query get modified, for example “get all pages except x pages”, or what really happens here?

I’d appreciate some pointers where to start so I can achieve this myself.