I interpreted the original article that their new node.js approach was wildly different than a server-based MVC framework.
Sure, they ended up with 20x greater speed, but never did they say that it was because node.js. They even provide a high-level detailed description of all the things they did with their new approach to achieve this performance.
"LinkedIn Moved from Rails to Node: 27 Servers Cut and Up to 20x Faster" should say something like "LinkedIn did a rewrite and rearchitecture that cut 27 Servers and increase speed aby 20x"