> But, what if they were actually NOT on the same partition?  Like
> with /usr/local on a different disk altogether?  Then it wouldn't
> work?  Is that what it comes down to?

Yup.   Basically, you're seeing ugly internal data structures
reflected in the user interface, which is non-ideal, but nonetheless
common enough that most of us fail to get indignant about it
anymore... :')

			       _MelloN_