Under 10.1, daily.out was created using...
# /etc/daily 2>&1 | tee /var/log/daily.out | mail -s "`hostname` daily output" root
... with daily.out being overwritten each day.
With Jaguar, this has changed to:
# periodic daily
Periodic's config file is located in /etc/defaults/periodic.conf - it executes the scripts in /etc/periodic/daily in order and appends to the file specified in the periodic.conf file. You can override the default behavior with /etc/periodic.conf, but I'm not sure how you'd go about configuring periodic.conf to overwrite the output log each day.