Well, there is no backbone network built to your principles.
Even when you build everything important fully redundant, the way the routing protocols work mean that a single configuration error or software bug can bring down the entire thing. See Level3 disaster a number of years ago.
There is also no backbone network built with enough vendor diversity that a single bug (such as, say, configs magically disappearing) won't have widespread effects. When it comes to fancier features, interoperability is still so crappy that you need to stick with a single vendor to use them.
The only alternative would be having two identical (but with different vendors) but separate networks in a passive/active configuration. And for the obvious cost reasons, noone even considers doing something remotely like this on a backbone-wide level.
Biting the hand that feeds IT
