Microsoft makes more than enough money to offer folk a reduction if they already have a copy of their O/S and want to install that on their new machine. I remember the day when you bought a PC then had to choose and buy and install an O/S. That all changed the day they sold licences to manufacturers to pre-install. I grudge having to pay twice for the same thing. I once HAD to buy a PC with Vista already installed and they refused to install XP I had to blow it away and pay extra to buy an XP licence.