Maybe this will clear up some misconceptions.
People who have upgraded to Windows 10 will be able to download media that can be used to clean install Windows 10 from USB or DVD. There will be no need to purchase a new copy of Windows 10 provided it is being installed on the same Windows 7 or 8.1 machine that was upgraded to Windows 10. The installed version of Windows 10, Home or Pro, will be the same as the version they upgraded to. However, people running an upgraded version of Windows 10 will likely need to buy a new copy of Windows 10 if they switch to a new machine or "significantly upgrade the device" - which Microsoft counts as replacing the motherboard.