No specific knowledge of how this works at HN, but I'm betting you're seeing caching behavior at work. Everybody logged in has potentially quite different HTML

No specific knowledge of how this works at HN, but I'm betting you're seeing caching behavior at work. Everybody logged in has potentially quite different HTML to serve up -- everybody logged out needs the same. The latter outnumber the former and, rather than applying a deceptively expensive sort-by-score on every pageview, it makes more sense to generate once and cache for "a long time relative to an HTTP request/response cycle."