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.
Historically also, they've pushed things out from a LTS release that could have gone in and made people wait for the next non-LTS release because they were too new or experimental. If it's good, it'll be in the next LTS, but if not, it won't and can be removed from the next non-LTS without impacting too much.
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.
> It literally remains stable for less time. Nine months instead of 5+ years, up to 12 if you pay them.
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.
I can see where you're coming from, but I think I'd prefer to describe practically all stable software as living in an unstable equilibrium in the usable region of state-space. When the stabilizing force of security patches, certificate updates, updates to new hardware requirements, and so on and so forth disappears the software falls out of the usable region of space into the, I suppose stable equilibrium, of unusable software. And this fall happens quite rapidly in the case of a linux distribution.
Applying the word "stable" to things in the unusable region of state space seems technically, but only technically, correct.
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.