Comment 1 for bug 12537

Thanks for your bugreport.

Update-notifer in itself does not reload the package database. It installs a
cron-job that does that nightly (actually it just set a apt configuration so
that apt does the updating nightly). The intervall can be configured via the
preferences menu in update-notifier. We don't want to display a icon if the
system is up-to-date.

I hope that answers your questions :) Feel free to reopen the bug if you are not
happy with this reasoning.
 Michael