By unix rules, the system normally should not remove anything from /tmp while running. In /tmp any program is supposed to be able to create files, write to them, and assume that files placed there will remain until removed by the owner. A program can not assume that the contents of /tmp will survive a reboot. That makes startup scripts the place for the system to do /tmp cleanup.

Some admins put in place some other policy they dream up, but the unix police will someday get 'em.

Putting /tmp on its own spindle, or at least a large partition, and mounting with the sticky bit set fixes most problems that non-unix policies are meant to solve. Going all BOFH on programs which don't clean up after themselves takes care of the rest.

Of course, users may clean up their own messes any time they like.