Why Node :
Modular - Even though they were using immediately invoked functions to create scope they realized the functions were themselves becoming global scope
Lightweight - Does not need to compile, Faster build times (15 min vs 2 seconds), Smaller foot print when running on the server. Allowed them to remove many runtime dependencies, Async allows them to server up requests much faster.
Technologies they use :
Express - Web App Framework
Dust - Templating engine