I suspect they have enough Lisp programmers for their needs at the moment. They're hardly 100% Lisp:
The backend database of QPX is in C++ and loads half of a 32 bit address space with route data, SBCL CL runs in the other half to figure out the "right thing" which is complicated in more than one way (e.g. a good result is not 100 fares doing roughly the same thing all within a few dollars; see the talk linked in the next paragraph).
The backend of QRES is Oracle RAC, the middleware is stateless and almost almost entirely in Clozure CL, although Dan Weinreb mentioned in his talk (NOTE, seems to be gone: http://www.youtube.com/watch?v=xquJvmHF3S8) that one team was using something else (Java, I think). The front end is in Java with a zillion web libraries.
They aren't Lisp fanatics ... I'm sure enough of them remember where that attitude got Symbolics.
