Why Nodejs?

It strikes a chord with the developer community, resulting in broad grassroots contributions.

It fills a need for light-weight event-driven web-scale integration tool. Javascript is a bonus.

It addresses a business niche: web shops adding realtime and push services (aka DIRT, data intensive real time [video]).

It is being improved rapidly for additional applications: Isolation of client sessions for greater stability. Mesh applications running on server and client OS, and on many processor cores.