It is certainly not specific to Facebook, but the scale at which Facebook is referenced across websites and apps is pretty unique (I can only think of a few key

It is certainly not specific to Facebook, but the scale at which Facebook is referenced across websites and apps is pretty unique (I can only think of a few key players like Google who would cause a similar load.) And to clarify a bit, the queries aren't "no longer being cached due to query failures", it's because their TTL expires and the resulting SERVFAIL from the next query (which fails) isn't cached at all.