If a language is 30x less efficient than another language then you would likely need 30x more servers. Many folk are simply not prepared to spend 30x more than they need to on hardware. It's the difference between 20 servers and 600 servers.
Case in point: "How We Went from 30 Servers to 2":
That's only true when you are using the full resources of one or more servers. If you are only using 1/100th of the server's resources, then being 30x less efficient still doesn't require any more servers.
That doesn't negate the point though, language performance matters at certain scales.
Case in point: "How We Went from 30 Servers to 2":
http://blog.iron.io/2013/03/how-we-went-from-30-servers-to-2...