Rails is turning into a framework that includes everything, including the kitchen sink. Personally, I prefer to use the best tool for the job and node.js seems to be a much saner choice when doing realtime communication, since everything in node.js is non-blocking. There are so many ways to shoot yourself in the foot if you develop large realtime systems in Ruby (or any other language that includes a lot of blocking…
First of all, there aren't really any decent solutions for the problem in Ruby. There's a few projects with great potential, but nothing really mature - when I needed to do this, I went with cramp.in, which hasn't been updated in over 6 months now sadly. Node.js would unequivocally have been the better tool for the job, but I didn't want to learn Javascript or Node for this one-off.
Secondly, even if there were mature Ruby equivalents to Node.js, or no impediment to me using Node, I can still see a lot of benefit to doing this in Rails. Personally I think it makes sense to be able to send events down to the clients and hook into the same models and business code you already have in place in the Rails app. (For certain use-cases, for example a project that's in Rails, is mostly a "regular" web app, but you want to give live updates for certain model changes, such as messages, ticket changes, new blog posts, whatever - obviously if the app is totally oriented around live functionality then node would probably be a smarter choice)
(I apologise for using the term "Node.js" as if its another web framework, I know that's not entirely accurate but I don't know enough about it to write more accurately!)