Maybe you look at the false examples :)
http://www.cisco.com/c/en/us/about/corporate-strategy-office... = Cisco Web & Email Security
The Source for the Server is now open source: https://github.com/ironport/shrapnel (python / cython /Pyrex)
And disqus had run mainly on Python before they moved some parts to Go-Lang
Many Gov's / Edu's run on Plone