do we lose words because they have no more use?

Ah, this reminds me of Dr. Bill's thread(s) on obsolete occupations from a while back:

http://wordsmith.org/board/showflat.pl?Cat=&Board=miscellany&Number=69547
http://wordsmith.org/board/showflat.pl?Cat=&Board=miscellany&Number=70168

Presumably once the occupation becomes obsolete, people no longer remember the word.