I dunno - most LFSP-people I know use multiple languages regularly, learn new ones as a hobby, and their "preferred" LFSP is just the top of a long list of skills. That's why we call them "smart people". ;-) Take a look at Programming Reddit - most of the Haskell evangelists are also quite fluent in Python and C and usually know Lisp, Ocaml, etc. too.
There do seem to be exceptions - Common Lisp in particular seems to be a LFSP where many of its leading practitioners only know Lisp. Smalltalk, too, but to a lesser extent since all the commercial Smalltalk jobs morphed into Objective C or Java jobs. But I don't really see Lisp as being at the top of the blub hierarchy any more - there's been 20 years of progress since then and some really interesting developments.
"Common Lisp in particular seems to be a LFSP where many of its leading practitioners only know Lisp."
The hardcorest Lisp hacker I know wrote the chapter on C++ in the UNIX Haters Handbook. He also wrote a C to Lisp compiler for the Symbolics Lisp Machines. (And he works as a C++ programmer right now. :-))
I'm not so sure. Most of the Common Lisp people I've met know Java. I can't think of a single one who doesn't know C.
Or did you mean Common Lisp people tend to have only that language as their LFSP, no matter how many LFMs they know? In that case I would agree - I definitely see CLers ignoring Ocaml, smalltalk, etc. For my part I guess it's because CL took a long time to learn fully and I need to build up some energy before I invest that amount of time in another LFSP.
There do seem to be exceptions - Common Lisp in particular seems to be a LFSP where many of its leading practitioners only know Lisp. Smalltalk, too, but to a lesser extent since all the commercial Smalltalk jobs morphed into Objective C or Java jobs. But I don't really see Lisp as being at the top of the blub hierarchy any more - there's been 20 years of progress since then and some really interesting developments.