LOL I was wondering about that too... but I found out this feature is actually even described in the manual!
Now WHY on earth would you need your car to beep on every full hour you ask? Well, in Germany, traditionally, all radio stations have a newscast on the full hour, which is always followed by a traffic update. (Yes, that's an ALL radio stations! No music for you for five minutes
So the beep is to remind you to stop off that tape you're listening to and find out what's new in the world... needless to say this feature is quite obsolete these days and was probably never even needed in the US.
Well, now you can go tell all your friends how German your car is