I'm pretty sure they are doing it for more money. The F8500 is the exact same TV as the F8000 but sense Samsung is using an all metal frame, they can market it as a more "premium" product. Due to this, I'm pretty sure that Samsung will be able to make a high profit on the F8500 than the F8000.
Samsung needs as much profit as possible this year. They spent a lot of money on developing their UHD and OLED TVs and due to the economy, there will not be very many people buying those sets. Getting high profits from the F8500 should help them recuperate.