Auto-analyse on insert operations

Hello,

I try to configure auto-analyse task with postgresql 9.4.
I have the following configuration (default configuration):
track_counts = on
autovacuum = on
log_autovacuum_min_duration = -1
autovacuum_max_workers = 3
autovacuum_naptime = 300s
autovacuum_vacuum_threshold = 50
autovacuum_analyze_threshold = 50
autovacuum_vacuum_scale_factor = 0.2
autovacuum_analyze_scale_factor = 0.2
autovacuum_freeze_max_age = 200000000
autovacuum_multixact_freeze_max_age = 400000000
autovacuum_vacuum_cost_delay = 20ms
autovacuum_vacuum_cost_limit = -1

With this configuration, I can observe that some tables are
auto-analysed, but some others are not. Even if there are millions of
insert operations on an empty table (all tables are in cluster mode).
In fact it seems that tables with update operations are the only ones
that are auto-analysed.
I'm quite suprised because the documentation says that daemon check the
count of insert, update and delete operations.
What could it be the reason ? Why tables which have only update
operation, aren't analysed ?
Are update operations really taken into account ?

Thanks,

Bertrand