It doesn't have to be this way. Apple doesn't have fear of breaking old apps sometimes, for example, and they are successful. I think that absurd backwards compatibility should be considered harmful and some breakage should be normal. It's always possible to install old browser into virtual machine, if content is so precious.
Apple doesn’t have the competitive pressure that I can take my broken iOS app and run it somewhere else as-is, or tell my customers to do that.
“It works in Chrome” (and previously IE) is a real issue and the browser that broke compatibility like that would have to be supported (potentially through the coercive power of its own market share - see the initial “any open source browser versus IE is a good thing” switching to “we need multiple browser engines, even if they’re all open source”) by the others or face irrelevance.
