Which suggests that even sites with a medium-to-large internet presence [...] can do so with "uninteresting" architecture
Absolutely. Hardware is evolving so fast (Moore's Law & friends) that we humans have a hard time to keep up mentally.
Go back six years in time and the traffic they're dealing would have required roughly 24 servers, instead of the 3 that they have today.
This is of course a rough extrapolation and six years seems like an eternity on the internet-calendar.
However we're quickly approaching a point where there's only two scales left to worry about: "normal" and "web-scale", with only a few hundred sites falling into the latter category.
Which suggests that even sites with a medium-to-large internet presence, which dominatre thier niche, can do so with "uninteresting" architecture.