io.js kept mum until the last moment before their release, with an invite-only codebase. io.js also took quite a while (> 6 months, far longer if you count the first fork attempts) to get to the first release and actually open their community -- turns out that producing a stable runtime is harder than it looks!
Let's call a spade a spade -- io.js is a great way to test out new functionality, but node.js is the stable, trusted version. io.js is the hype.
It remains to be seen whether io.js will prove itself profitable for adoption.