Sounds intriguing - can you elaborate on why this combination is favoured in particular? Or point to an article that discusses it? It's hard to get widespread adoption if it's not accessible...
incidentally, google protocol buffers seems similar to http://en.wikipedia.org/wiki/Abstract_Syntax_Notation_One (ASN.1), which predates XML, but didn't take off.
And AMQP was chosen for the transport layer because it handles persistent messages, transactions, all the routing, buffers messages, etc., etc. I'd have to implement all of these myself, had I chosen thrift.
This is how I ended up with RabbitMQ and ASN.1.
Therefore, XML became more popular than ASN.1. I think the successor to XML (and SOAP etc) will be more human-friendly than XML, rather than more efficient.
That's not to say that extremely efficient techniques don't have a place (they do) or they're not cool (they are).