Most likely it means that there's a newer V8 involved. Otherwise there's not a tremendous delta.

This is bigger news for io.js than it is for atom. <<< I think is the lede.

Yes. It is arguably larger news for io.js.

However, that io.js ships with v8 4.1 is quite a large step ahead for dependants, not just for language features, but also under-the-hood stability and performance.

Of course, there is also everything that node 0.11.x has, plus a release schedule to match Atom's own release cadence. :)

io.js also ships with the node.js active core developers...