Have you heard of FFIs? Foreign function interfaces? You can call ANY OS system call from Lisp, and for user-mode shared libraries you can just load them and call their functions just as easily.
Look for some applications your code needs to be as fast as possible. When your company is writing the software and spending 50million / year on HW taking a slight speed hit to use your favorite tool is not always an option.
PS: Consider how much money Honda spends on processing power for their engines and how much a 5% speed hit would cost them to fix by buying better HW.
http://www.sbcl.org/manual/Step_002dBy_002dStep-Example-of-t...