There is nothing built into the Personal LaserWriter engine that counts
printed pages. A mechanical counter would add cost and be vulnerable to
tampering. An electronic counter would require additional logic that may
not otherwise be present.
About the only laser printers with a page counter are those with a built-in
PostScript interpreter. Implementing one on a PostScript controller is
relatively trivial, because the requisite logic is already in place. The
count is usually used to determine mechanism wear.