Actually DIGEST and INDEX recipients <are> counted.  NOMAIL recipients
aren't, and as Ben noted, if you use TOPICS then your recipient count
will vary depending on who is subscribed to each topic.

In earlier versions (1.8c or 1.8b and earlier, I can't remember offhand)
the count did reflect only non-digest and non-index subscribers who were
set to MAIL (ie those who got individual messages when a posting was
processed).  This was changed either in 1.8c or 1.8d to reflect everyone
who got the posting, either as an individual post or as a digest or
index, even though some of the people reflected by the count wouldn't
get their copies until the digest was cut (and even though the INDEX
subscribers only got an index of subject lines).  I'm fairly sure this
was discussed either on LSTOWN-L or LSTSRV-L in the past couple of
years, but it's Sunday and I have better things to do than search
for it :)

Nathan