I don't remember PoF being famous for that, but they got a lot of bang for the buck on their serving costs.
What I do remember, is that it was a social data collection experiment for a couple of social scientists, that never originally expected that many people would actually find ways to find each other and hook up using it.
I miss their old findings reports about how weird humans are and what they lie about. Now, it's just plain boring with no insights released to the public.
POF was also run by a single dude until he sold it for some 600 million dollars!
HN is written in a lisp variant and most the stack is built in-house , it is not difficult to imagine efficiency improvements when many abstraction layers have been removed from your stack .