You are forced to update the launcher and game if you reinstall the OS or get a new computer, and most likely it'll just auto-update without asking. There is no way to download or archive old versions.
> You are not entitled to subsequent updates or upgrades.
Then those should be truly optional and the store page should visibly state this limitation while keeping the purchased version accessible.
Worth noting that when I purchased minecraft back in 2011, the store page did in fact (according to archive.org) say:
“When you purchase Minecraft you do so as is, be it in the early stages of development or already fully released. Subsequent updates are only an added bonus and not a guarantee, as icing on a cake. Purchases during the development of the game are discounted and include the full game upon release.”
and
“When you purchase a game from us, you fill in your personal/company details. You agree that we store and use your information in our organization to complete the agreement towards you. You have the right, according to the law Personuppgiftslagen (PUL) in Sweden to know about the information registered about you. If it is wrong, insufficient or irrelevant you have the right to make sure that it gets corrected or removed.”
> You are not entitled to subsequent updates or upgrades.
Then those should be truly optional and the store page should visibly state this limitation while keeping the purchased version accessible.