It's interesting that you mention Python, because obviously the RoR equivalent there is Django which leaves something to be desired when it comes to DSLs and expressive APIs. Symphony and Laravel also come to mind here, and I guess Spring in the Java world. I think it's difficult to argue that the creation of a major web framework hinges on being able to express things in a nice DSL.
Rather, I think the truth is that server-side Javascript tends to be used in a different way to Ruby - generally Node projects that I've worked on are much smaller (and often coupled with other similarly-sized services), and are often just minimal APIs designed to act as a middleman between a database and a front-end application. It's not an issue with missing expressivity, but rather a tendency not to need (or at least, not to want) the full-featured powerhouse that is RoR.