And if that one-time purchased software stops working at an arbitrary date, it should be subject to the same rules. Especially online software or software requiring servers to run.

You can still offer limited-time subscriptions, of course, and you can extend the minimum deadline for your server-dependent software to free as often as you want, just make sure people know what the deal is when they buy your software.

DVDs and other media also aren't yours to buy, they're just licenses and a physical container to use that license. You can buy software the same way you can buy a DVD, and you can rent software the same way you can rent a movie on a digital storefront.