This doesn't really pencil out..."your binary, and the libraries it uses" can easily get into the GB when you include components like the .NET framework or java base class library. I don't know exactly how large a fully-loaded NPM repo with warm cache or warmed-up rvm installation directory are, but it isn't tiny.

Second, POSIX is a standard for how the operating system API works that has nothing to do with what packages are installed -- and it's a pretty low-level API, for doing stuff like read, write, fork, exec, etc. This isn't what's adding bloat.