[ ... ]
   i.e., in using if_unit & if_name, one might assume that "le" #0 and "le" #1
   are somehow related.

who cares if they are related ?  "Maybe I'm Missing Something ..."
   
   The implication of "if_xname" is that the number for the interface is
   not needed to indentify an interface, an interesting concept but is it
   really that much of a problem that we want to make portability of
   applications that much harder ?  (any programs like netstat will have to be
   altered to deal with this, for example).

hmm?

what does it matter what the interface is called ?

.mrg.