Attached Link: http://wiki.blender.org/index.php/Dev:Doc/New_Dev_Info

*"Most of the blender core is written in C, using an object oriented programming system called BlenderDev/OOPS. Library API's are always exposed using C, even if the library is written in C++. Frequently, but not always, new functionality is written using Python (modifying the python API by wrapping the C if necessary) and then after working out the usability issues and testing the functionality out--- it is ported to C for speed."* 

 As far as I can tell from an admittedly brief perusal, Python is only used as the scripting API language for Blender - as it is for Vue and Poser, or JavaScript (or even VBScript) is for Photoshop.
I emphasize only because scripting can add immense power to an application. They're just not using it to do a lot of the the heavy lifting - apparently. So, I wouldn't say Blender is a case for Python's speed appropriateness for a 'whole application'. But I'm no expert on Python or Blender and just a country programmer.

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