You know how manufacturers will add a feature that 90% of woodworkers will never use.... A blade guard on a TS comes to mind. If they did not include the slot on a router table they would lose sales. I have never used a TS blade guard but would not buy one with out the guard, strictly from a resale point of view.
IMHO the only use for the router table slot is to provide a spot to mount the feather board.