[jolux]

> The vendor could choose to allow backwards compatibility, but often chooses not to.

This too entails a tradeoff: either the old software sits around in the system collecting defects, or it ends up supported indefinitely and the amount of work required to cut a new OS release increases without bound.

> Sorry, but when I write a program in 2010, I kind of do expect it to still work on the exact same hardware in 2020. I don't think that's an unreasonable expectation.

Unreasonable compared to what? In the abstract it’s not unreasonable but computers are quite an unreasonable environment to begin with. Their capabilities change dramatically every few years, and computers on the internet especially have to withstand essentially constant attempts at intrusion and abuse.