Sure, not a stupid question at all. The presence of multiple TWR and APP/DEP freqs is b/c it reduces controller workload on aircraft departing in and arriving from a variety of directions on many runways. There aren't really two towers at O'Hare (to my knowledge) (although there are at many other airports), but having two freqs for the twr greatly reduces twr controllers' workload. This was brought about after a runway collision between a USAir 737 and a Skywest Metro on an LAX runway that was caused by a controller's inattention. That inattention was caused b/c the controller was working both the north runways (24R/6L and 24L/6R) and the south runways (25R/7L and 25L/7R). Similar systems of two or more twr and app/dep frequencies are in place all over the country. In example, ATL has 2 freqs for each local control facility (twr, app, and dep), each divided into south and north vector areas. Hope this helps.