Yeah, the JS world currently is very pro-modularization, but I already saw some discussions on Twitter from the React/Flux people how that creates too big barrier of entry for the newcomers. One of the things that draw people to Angular is that it has almost everything that you need included - it's easier to say to someone "just use Angular", than "try React, with Redux, and Router, and Webpack - it will take some time to configure it, but it's worth it".
Well, it has it's benefits.
I don't like Redux and I like Reflux so it allows me to do that.
Then again Rails does let you switch out compatible parts. By compatible I mean if it adheres to "Railties", e.g. using ActiveModel for replacing Pgsql with MongoDB.
Even React, Flux, Router and etc comes in several parts.
I know railties are modular but at least they come from the same project and repo and update together.