But everyone sees the same edited version when not logged in, which is the vast majority of users, so you can just throw a huge cache in front, which is what th

But everyone sees the same edited version when not logged in, which is the vast majority of users, so you can just throw a huge cache in front, which is what they do. And most edits only touch one page, so the churn is tiny relative to the cache size. This is a much easier service to reliably engineer than something like Twitter. For SRE purposes, Wikipedia is mostly static.