Gah.
[jake@jace]/bin% ls -lhd /bin
lrwxrwxrwx. 1 root root 7 May 22 2012 /bin -> usr/bin/
I'm running Fedora 17. Apparently `/bin` is symlinked to `/usr/bin`. And of course (and quite rightly) `find` and `locate` ignore symlinked directories to avoid result pollution.