1. It literally remains stable for less time. Nine months instead of 5+ years, up to 12 if you pay them.
2. They apparently have a history of testing changes in it.
3. They appear to only sell things like livepatch and extended support for LTS editions, and products you pay for are implicitly more stable than products you do not.
Or to use Ubuntu's own terminology: "Interim releases will introduce new capabilities from Canonical and upstream open source projects, they serve as a proving ground for these new capabilities." They also call LTS 'enterprise grade' while interims are merely production-quality. Personally I see these as different levels of stability.
Isn't "stability" in this context a direct reference to feature set which stays stable? When a version is designated stable it stays stable. You're talking about support which can be longer or shorter regardless of feature set.
When they stop adding features, it's stable. Every old xx.04 and xx.10 version of Ubuntu is stable even today, no more features getting added to 12.10. When they stop offering support, it's unsupported. 14.04 LTS became unsupported last year but not less stable.
These are orthogonal. You can offer long term support for any possible feature combination (if you have the resources), and you can be stable with no support. In reality it's easier to freeze a feature set and support that snapshot for a long time then chase a moving target.
Applying the word "stable" to things in the unusable region of state space seems technically, but only technically, correct.
If you have a problem with them, 20 other people have had that same problem before you did, two of them have posted on Stackoverflow and one wrote a blog post.
OpenBSD and Illumos may be cool, but you really need to know what you're doing to use them.
That said, the underlying structure is still Ubuntu centered. I also like Ubuntu server, even through I don't use snaps, mostly because the install pre-configures most of the initial changes I make to debian anyway. Sudo is configured, you get an option to import your public key and preconfigure non-pwd ssh, etc. I mostly install ufw and Docker and almost everything I run goes under Docker in practice.
Unofficially any serious user knows to stick to LTS for any production environment. This is by far the most common versions I encounter in the wild and on customer deployment from my experience.
In fact I don't think I ever saw someone using a non-LTS version.
Canonical certainly has these stats? Or someone operating update mirror could infer them? I'd be curious what the real world usage of different Ubuntu versions actually are.
The above is absolutely what happened in this case. The package was at revision 0.1 throughout the release cycle, then 12 days before the final release, 6 weeks after the freeze and after the beta release, they changed the package to 0.2 with no notes other than "new upstream release". Nobody had time to try it, they just shipped it out to everyone literally without even trying it once.