I would have been surprised to learn it was on 50 or 60 servers. I'm a little bit disappointed to learn that it requires 9, as I had thought of them as one of the last bastions of scale up rather than scale out, but 9 is approaching a large number.
I think the complexity costs of scaling out are underestimated; or rather, they're just accepted as a fact of the matter, like there isn't an alternative. More moving parts in the name of redundancy etc. usually makes things more fragile, without very careful design and implementation.
Interesting that you bring up GitHub. GitHub was probably the most unreliable service our startup used before we moved to Stash. You could count on it being down for a few hours every month, reason given usually "DDoS". We moved to Stash for contractual reasons relating to security and ISO certification required by our target sector, finance, but I could see us having done it for reliability too.