Ah, yes -- instead of being willing to work on improving one of the existing scientific Python front ends and/or libraries (Sage, IPython, SciPy, etc.), let's invent a new one that will end up competing for time and resources with those that already exist.
Even though most of these choices are free, they still possess a strong component of not-invented-here (typical of paid software), and the Balkanization of technical Python options and environments.
Having said all that, and just to make this interesting, the features page shows some pretty nice stuff:
http://code.google.com/p/spyderlib/wiki/Features
