You don't own games generally. It's always a license for software use. You may own the game, if you buy the company and the license is fully under its control.
Software is not a product. And there is no guarantee you will be able to run it forever, even if you made a copy of your entire setup. It's especially the case with Windows, because it's bound to a specific hardware that will break one day. Microsoft also cares less and less about gamers (see what they do with their operating system for consumers) and they have a way out with XBox. My bet is that Windows is not making money for Microsoft anymore and it will degrade more and more. Gabe knows it and has a strategy against it. If you're a gamer and want have games on PC, use Linux and support the good cause.
I've had some fun about thinking how much overlap you need. And while playing with the thought to maximize it, I came to the conclusion that you can just have two keyboards, for each hand one.