Yes, anything that only uses posix functions is less fragile, obviously. It's the user space libraries: UI, sound, notifications (for those last two, it's not just the API's that change, it's complete subsystems being pulled from under you), ...
Look, I'm not saying there is no Linux software that doesn't keep working, it's the overall time you spend over the lifetime of your software to keep up with updates in its dependencies. I don't see how anyone can reasonably argue that Windows isn't a whole lot better than Linux at that.
(I've been using Linux since 1998, I'm not new to this game)
What this have to do with reliability of windows as a platform.
Reliable platform means, that new versions of OS do not break your old program. Which is true for windows.
Of course, as OS becomes more capable, it's possible to write programs that can't work on less capable older versions. But even then, windows tries to add fallbacks so that most new programs still work on old versions.
Quite a lot of the core tools (shellutils) are 20+ years old with only minor updates.