moot point. it will probably cost you nothing, because if you are running XP, you aren't buying this. If you are running XP, then you are buying a new machine and chances are it will come with either a recent OS or 10 itself.
People with old machines building their own new machines and getting 10 will be in the minority. Tip: get a cheap 7/8.1 license to upgrade for free to 10.