RoR allows lots of HN-types (hackers, people prototyping web business, etc.) to build products quickly. In fact, that's exactly what TFA is an example of.
I'm actually constantly surprised at the number of HN readers who seem to hate on RoR out of general principal.
A lot of the HN crowd dislikes PHP, and can point to dozens of reasons why: no consistency in the standard library re: naming conventions, order of arguments, etc; poor abstractions; up until recent versions, a lack of namespaces or late static binding, and so forth.
A lot of the HN crowd seems to dislike Rails, but I've never once seen someone post a objective reason why. Philosophical differences I can see -- maybe Rails isn't for everyone. But the majority of the anti-Rails posts are FUD at worst, and misinformed at best.
