I think it hasn't caught on yet because there's no (last time I was around anyway) solid, decent, recommended deployment strategies.

It was once suggested to me on IRC to use only one instance of a node app because it's "non-blocking"... I'm serious: "why would you need more than one?".

Obviously you can deploy well enough using a monitoring app to keep up as many workers as you want, but compared to stuff like passenger it's just not mature enough.