IMHO these guys just didn't architect and configure .NET to suit their loads. ADO.NET connection pool is adjustable, it's trivial to setup a (NodeJS style) single DB connection per app pool.
They seriously must have been doing something wrong. We scale to 2000 requests a second on a good day on one not very hefty quad core SQL server 2008 box with 16Gb of ram and 2 front end web servers and a virtual active directory host. The requests are between 2-4 SQL queries a hit as well and can return hundreds of rows with 6 way joins galore thanks to nhibernate. Latency per hit is always less than 80ms.<p>We've done literally no tuning as well. It's all out of box. It just sucks up the requests and spits them out with a smile.
Nice write up. Things have certainly changed since the first time I saw benologist comment about the original architecture on HN. At the time I was excited to know there were other startups using .Net.