With PHP and PostgreSQL we could scale up, but it felt really hard and gave us many sleepless nights. Using Node.js with a MongoDB backend scaling up is quick and easy; but because Node can handle more traffic, you don’t need to as quickly.
It's interesting to read an experience where Node's performance largely pays off when building traditional sites. I've often read that Node's performance really only pays off when building realtime apps. Maybe I misinterpreted, perhaps it was meant more as the large set of features provided by frameworks like Rails/Django transcend Node's performance boost?