Yes, I just went through the same thing. The BSM is now standard on the GT. I was ticked off when I found I was charged for it as well. ($180 invoice I think?) However, the dealers explanation made sense: Even though it is now standard, it costs money so the customer is going to pay for it. However, car companies don't change the base price of cars midyear. Therefore, they charge you a line item fee for the BSMS. Next year, it will be built into the base price of the GT and the GT will go up $180.
Even though I don't need the BSMS, it is still nice to have, especially for my wife.
(If you set the mirrors up properly on almost any car there are no blind spots. Move the drivers mirror outward so that you cannot see the side of the car unless you bend your head halfway over to the window. Now let a car pass you from behind on your left side. First he is visible in your rearview mirror, then there will be an overlap where he is visible in both the rear and the driver's mirror, and he will continue to be visible until you can see him through the window with your peripheral vision.)
That being said, perhaps one day I will not have the mirrors adjusted perfectly, and the blind spot indicator will beep and save me.