I haven't put much thought into this until now, but it seems odd that there is a /var/tmp and /tmp directories for most of the linux distro's I routinely use ( Ubuntu, Centos, Redhat ).

Is there any semantic difference between the two, like when whoever designed the first file system layout, he or she thought "Not all tmp file's are created equal!"

The only difference I've found for centos, is that /tmp routinely scrubs out files older then 240 hours while /var/tmp holds onto stale files for 720 hours.