I guess I am misunderstanding, but on our lowly HP LaserJet 5N with a
   10baseT network connection, I just use a remote-printer-name of "text"
   for the plain-text queue and "raw" for my postscript queue.

That works fine and is exactly what some of my queues do.  The problem
is that if you want to filter the job before you send it to the
printer (and are using stock lpd which only filters jobs going to
local printers) you need to fake out lpd so it thinks it is talking to
a local printer and will filter the job.  Hence the lp=/dev/null in
the entry with the if=/print/filter.  The filter needs to take care of
respooling the (now filtered) job to a new queue.

Cheers,
Brook