authorized dealers have the discresion to fix items on a car based on "good will". like if you have a 36,000 mile powertrain warranty and your tranny takes a dump at 37,000 miles. some dealers may still honor the warranty. and the manufacturer WILL reimburse the dealer for all warranty claims, so the dealers isn't losing any money anyways!
the room mounted focus antenna was designed to be removed for car washes and such, otherwise they wouldn't have put a thread in it, right? if your antenna did truly fall off like you said, your dealer should fix it. i think your service manager is just being a jerk. you should try another dealer. good luck.