It's easy for non-ops people to install packages, but I'm not sure it is easy to do large scale deployments. I'm not hating on npm, but there is still a lot to do with managing all of the dependencies in a way that makes it easy to deploy consistent packages. Pip doesn't solve this problem either, so it isn't unique to npm.
There are some tools for using npm for large scale deployments. Packages are scoped locally to an app, you can bundle them if you want, and there's a "shrinkwrap" command for making sure the installed deps are exactly the same every time. Personally, I would either go with, "peg every version to an exact semver" or "bundle ALL the deps".