If the inn package is installed, the related cron jobs are
apparently always enabled and always run, even if I don't
actually start inn as one of the boot daemons. This is
fairly disconcerting and clutters up the logs ...
Yes, this is true. If you install Inn then the cron jobs are inserted
into the system, even if you never run the process. One option is to
uninstall Inn, in which case the crontabs will also be removed. Also,
you could disable the crontabs when you do not want those jobs to run.