It's not entirely true what you write ('ve seen button-based navigations as well, and sometimes even 2 columns of those buttons!), but let's just see the necessities:
Take an iPhone. Some phones are wider than that but let's just assume an iPhone is representing an average width/height of any mobile device. (see this Wired article, and this linked Flurry report for sizes of devices currently in use)
Most people seem to use their device in portrait mode (see this UXMatters article)
Imagine any kind of body copy half-width of that screen width. I guess it'd be uncomfortable, perhaps even unreadable for some people.
So therefore, body copy has to be of full width.
With navigation, you can essentially do the following:
- Place it at either at the beginning or the end of the page
- Hide it, leaving only a signifier (new term for affordances) - that means, a small icon or button or "NAV" or "MENU", when you click, it replaces part of the screen and shows navigation
- Expecting users to use learned behaviour and instead of a signifier, use a kind of a gesture - all "swipe from here to here with N fingers" stuff
- Combine these two, leave some affordance, but also allow gestures
With these, you have plenty of opportunities. Like, you could even employ Windows/Metro-esque panorama layouts:
The trick Microsoft uses is to use the edge of content as a kind of signifier / affordance.
Of course, that's not always a solution, and if we're talking about usual content pages - where users are likely to be interested in a given article - it's not always feasible to load next / more views.
The big idea of Mobile First approach was to remove clutter and think in chunks of information and context.
It's not about grids. As you see, you can have a large grid, of which at any given time, you only show a portion of.
It's about understanding that content is king, that the user came for the content, and it's okay that navigation needs more effort in order to keep the view focused and clean.
You don't go to a website to navigate. You just want to find what you're looking for and anything else that is there is essentially clutter, wether we, dreamers of those sites, like it or not.