[CentOS] cron mystery

I've just noticed that cron.daily, etc,
do not seem to be running on my CentOS-5.4 system.
The scripts in /etc/cron.d/ all run fine,
but those in /etc/cron.hourly, etc, seem to be ignored.

I see that according to /var/log/cron
these commands are seen, eg

Feb 28 18:01:01 helen crond[6680]: (root) CMD (run-parts /etc/cron.hourly)

but none of the scripts in this directory
seem to be touched.
I've tried running them by hand, and this seems to work fine.

Is there some problem, or subtlety, about crond under CentOS?

-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland