We’ve talked here before about how the convenience of buying movies digitally is in place of the guarantee that you’ll be able to access it for a long time into the future (see: What happens if the streaming company you “own” a movie or TV show from goes out of business? Yes, you lose it).
When you buy a physical disc — Blu-ray, DVD, etc — as long as you have a player to play the disc and the media isn’t damaged — nobody, thieves aside, can take that away.
Digital licenses are not currently and never have been permanent. Amazon is admitting what’s already stated in their TOS (Terms of Service):
So, keep this in mind that buying a bunch of movies digitally doesn’t necessarily mean you’ll be able to watch it tomorrow, next week, next month or next year. Buying the physical media is not exactly without obsolescence, just go back to betamax, laserdisc, HD-DVD as formats that have been replaced by newer, better technology.