I feel like a lot of things, at least in ruby world where I mostly work, have gotten a _lot_ better in the past few years.

"Strictly"? Well, backwards compat mistakes can happen, but mistakes can always happen. Other than that, it's the difficulty of knowing what is the "public API". It's a time-consuming and difficult task to be clear about this. But I think semver has spurred people to try harder and get closer.