Hi Mandelbrot,
Searching for File Hashes doesn't scale well in the current Gnutella Network, which means they waste lots of bandwidth for all Users.
(Check
http://gnufu.net - Query Routing Protocol for more information )
To do this, LW would have to run two seperate networks: One for Hashes (with a completely different organisation) and one for normal searches (for which the current Gnutella Net is strongly optimized).