Your rear seat doesn't fold down because you have a convertible and the top is right behind the rear seat. Its my understanding that all the hardtop GTs have fold down seats, I don't know about the v6s(never even looked at one close). The first time I ever saw a fold down back seat, in something other than a hatchback car, was in an 89 Mercury XR7.
You can probably go to
www.ford.com and look at all the options, you can actually build your car with the exact options you want.