Well, its hard to tell not being a haskell advocate, but the people building the systems were haskell experts with years and years of that being their only language and were extremely particular about the implementation, which is part of the reason why they justified the 10 requests per second part, is because it was "done right". My understanding is that haskell is designed is such a way that certain things are impossible to do any way but the "right way", so its also just fundamental by merit of the fact that they were using haskell to solve those particular problems. But it was mostly clout and the fact that the implementation was so thorough and the people building it were like phd level experts in haskell/category theory.