It seems to me that "on" is often incorrectly used in place of "for". As an example I could be waiting at the station for a train. Many people would say they were waiting on a train, which which implies the train has arrived, they got on it, and are waiting on the train for it to go somewhere. The most common use might be as a waiter in a restaurant waiting on a customer. Literally the waiter would be sitting on the customers lap waiting for the customer to order, finish his meal or ask for a check. The waiter, or waitperson, is actually waiting for the customer to order, request another glass of wine, or ask for a check. The customer, meanwhile, is waiting at his table, on a chair, for the waiter. Interestingly, I hear this in conversation but seldom see it in print.