Well, Google got good at large scale rollouts, because they are doing large scale rollouts all the time. _And_ most of the time, the system they are rolling out is a small iteration from the last system they rolled out: the new GMail servers look almost exactly like the last GMail servers, but they have on extra feature flag you can turn on (and which is disabled by default) or have one bug fixed.

That's a very different challenge from rolling out a brand new system once.