[irahul]

> What this says to me, a non-RoR user, is that it's harder to build websites with Java than with RoR, but if you pass a certain (very unusual) level of traffic, you'll wish you'd made the extra effort; otherwise, you'll be glad you didn't. (Extra effort isn't free.)

Twitter hasn't phased out Rails, it has replaced background services written in Ruby.

> Fine, but what I wish I understood was why RoR is so popular to begin with.

That is hard to explain. You will have to try it out yourself and compare with whatever you are currently using.

> why isn't one of them Python on Rails

As other responses pointed out, Python has Django. And no, Django isn't rails inspired. Django was developed independently. Also, the languages and philosophies differ significantly to have a Python on Rails.