Do they really need to develop a new environment? The IPython notebook environment can be adapted to different underlying language kernels--I think they've gotten the notebook at least partially working for Ruby and Julia. Why develop a whole new front-end just for R, instead of working with what's already an effective and tested environment?

I've had several conversations with R folks who insist that RStudio + Knitr does everything the IPython notebook does, and I feel like I've had a hard time conveying why I like the notebook for data exploration, prototyping, and demoing.

E.g., the R notebook linked to below looks neat, but it's still just markdown compiled to a static document. That's a different workflow--not a better or worse one; but certainly different.