This only matters if you need specific features from those libraries in your web app, there is no adequate library in another language and you can't use the pyt

This only matters if you need specific features from those libraries in your web app, there is no adequate library in another language and you can't use the python library without strong integration in the app. Ruby's domain is primarily the web and web systems, and when it comes to that area, Ruby has an vibrant ecosystem with plenty of libraries and tools that don't have python counterparts. Ruby developers have also readily borrowed good ideas from Python. For vast majority of web development, these kinds of things matter more than the existence of something like scipy. Each language has its strengths and weaknesses with regard to the quality and quantity of tools directly related to web development.