Why oh why are main nav items rendered in rows containing 2 items?

I can't see why the main nav items need to be rendered in rows of 2 items each. It makes no sense to me as they're only ever displayed one below the other. When I add another menu item of my own that's accessible to anon users then the home page menu item padding is all messed up as I don't think it was ever tested with more than 2 anon accessible menu items. To override this markup and css is a total pain ... Is there a valid reason for this overly complicated menu item markup?