Sounds like it really ought to be built into the delete script... but I can see where people who delete "old" posts don't necessarily want users numbers to go down... if they are building a history.
There really should be a checkbox on the delete screen to decrease the post count or not.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.