But was it really necessary to switch from Rails to Express/Node in Product Hunt's case ? That's why I'm kind of surprised.
I know the CTO of product hunt - he wouldn't switch the tech stack for no good reason. They already used node ~1-1.5 years ago for some parts of the site. I'd guess that they found out that it works good for them and they switch completely over to node, which also removes some rails legacy code they had.