That's why I always try to buy from Gog. They have a commitment that you should be able to download the game, back it up to whatever media you like, and play it

That's why I always try to buy from Gog. They have a commitment that you should be able to download the game, back it up to whatever media you like, and play it without an internet connection. Of course this means you can't find everything there, but they still have a good selection and I think it's an important mission. The internet is surprisingly ephemeral.