autovacuum 'stuck' ?

When reviewing the vacuum logs, I notice that on any given day
autovacuum only seems to touch four of the tables in one of our
schemas (not counting toast tables). However, if I look at the
pgstatspack output for the same day, I see that there are plenty of
other tables receiving a high number of inserts and deletes. How can I
tell if autovacuum is accurately choosing the tables that need its
attention (these four tables apparently) or if autovacuum is simply
never making it to the other tables cause its too busy with these
tables (my suspicion)? This is on 8.3.7 with the following settings in
postgresql.conf:
autovacuum = on
log_autovacuum_min_duration = 0
autovacuum_vacuum_threshold = 250
autovacuum_analyze_threshold = 125
autovacuum_vacuum_scale_factor = 0.2
autovacuum_analyze_scale_factor = 0.1
autovacuum_naptime = 5min

Any/all other information can be provided as needed. TIA, again.
--
Douglas J Hunley, RHCT
doug(dot)hunley(at)gmail(dot)com : http://douglasjhunley.com : Twitter: @hunleyd

Obsessively opposed to the typical.