It is not. There are all over internet tutorials on how to install DX 10 and beyond on XP.

That is not the MS native implementation which requires the new driver model. MS ditched the old DirectX redists after 9.0c in 2004 and since then only updated D3DX. Sure there is the Platform Update for Vista, but that is only possible because Vista already have the new driver model and it uses a completely different installer.