Postmaster not reporting number of connections correctly

I've been using 8.0 ever since beta 1, and am currently on 8.0.1. I have
noticed (in each version) that the number of records in the pg_stat_activity
table is not always representative of the number of connections to the
server. That is, we have an installation at a client's site that runs a
nightly batch and reports the results of the run back to us. One of the
items reported is a count of the number of records in pg_stat_activity (a
section of the batch is dependent on whether or not any client connections
exist). Every now and then we'll see that the number of records in this
table is zero, when there should always be at least one since our batch is
connected when it runs. I've also seen this myself when querying the table
(zero reported connections).

Is there a better way of obtaining the number of connections to the
postmaster?

Much thanks!