If you bought Windows XP in recent years, the DVD already installed Windows XP together with the latest available Service Pack. If you buy Windows 8 right now it automatically installs Windows 8.1 from the disk. It will work similarly for Windows 10, regardless of the nomenclature they are going to decide on.
I'm thinking of this as something similar to how OS X releases work. There's a way to get the distribution you need without having to start from OS X 10.0 Cheetah and upgrading all the way.