It does. File system, databases, requests, whatever. At least I am not aware of edge cases currently. Only be aware that C++ node.js modules are incompatible with node-webkit, you have to build these modules with nw-gyp. A little inconvenient, but should work fine.
Neat. An Objective C bridge to access OS X's frameworks was specifically what I was thinking of, and it looks like there is one: https://github.com/TooTallNate/NodObjC