Another scenario just occurred to me. Imagine that I have WP installed on a development server and I'm, yes, developing a website. And here comes a new major version that breaks plugins I was counting on, changes default settings I was taking for granted, subtly alters the behavior of a key API function...

At least it's not as bad as if it happened in production. But as a developer I'd be very wary of ever using the platform again after such an incident, no matter how much I like it and even depend on it.