Bookmarks bar usually holds bookmarklets, which are useless as Favorites items on a start page so this is why we made this distinction, giving the users more power.
Vlad I would like to know what users actually use the bookmarks bar as compared to the start page. I would like to see everything listed in my "Bookmarks Bar" in the start page, not have two separate folders which create clutter of which one is barely used.
An alternative would be to automatically detect and hide bookmarklets from the start page. This might create confusion though.