Totally different runtime. There's no way (short of IPC) you can interface between node.js and Javascript for Automation. I suppose you could write a CommonJS Modules-compatible shim for Automation, but libraries assuming a node-like environment just wouldn't work.
Yeah, that's what I assumed. I guess it might make 'developing' slightly easier thought, keeping in the same language with Node + Automation, rather than Node + AppleScript.