Wittgenstein has a wonderful metaphor of language as like an old city. The oldest parts are crooked, winding, organic. On top of and growing around old bits are the new, modern, rationalized parts.
I think the social structure is like that, too. There is an old, crooked organic structure based on an honor/shame culture. We see it especially at the top, with its residue in Old Money. And we see it at the bottom, where gangs and slums reproduce honor/shame warrior bands wherever bourgeois order is ineffective.
On top of this old organic structure, though, a modern, rationalized grid has been laid. The main mechanism of rationalizing the social structure is the educational system. And the main tool for creating social closure differentiating one stratum from another are educational credentials.