MS has a pretty easy out on this one. They are not bricking machines, disabling software, or locking accounts. They are simply saying "if your hardware does not meet our requirements you cannot connect to our servers". It's a perfectly legit response regardless of why they are doing it. If they deem any users hardware not being fit to connect to their servers they have the right to denying access. It's something WoW/Blizzard has done for a long time and they don't get sued because there's nothing wrong with it.