I'm biased because I did some work on Colossus for a few years, but it's my opinion that Google's main advantage in its ability to build complex distributed systems is Colossus (and GFS). The Colossus layer is the point where a lot of systems actually take care of the CAP theorem, and because Colossus does it so well they almost don't have to worry about it at all.

Ceph, Hadoop, scale-out ZFS, and others that came afterward got the idea of distributing a filesystem but sort of missed the point that GFS/Colossus's great advantage was that it's so damn good at being a distributed system, and has been tried and tested through a lot of different kinds of failure modes.