Two things: one, the quality of "developer released" packages varies wildly, so it's hard to make a global policy. Two, a distro means integrating many packages. An upstream package change might be 100% reasonable and at the same time break existing users because (e.g.) of a feature removal that went through a normal deprecation policy for that package, that distro users are obviously not aware of.
Ubuntu is supposed to integrate and add a QA layer on top of upstream packages. Just pushing any so-called stable release of upstream packages isn't going to improve the situation, even if it might in specific cases.
Personally, I don't see a way out. The very fact that a distro is an agglomeration of independently released packages means that there will be breakages like the ones you describe, because every package has its own concept of stable release, development cycle, feature deprecation, old version support, and so on.
Ubuntu is supposed to integrate and add a QA layer on top of upstream packages. Just pushing any so-called stable release of upstream packages isn't going to improve the situation, even if it might in specific cases.
Personally, I don't see a way out. The very fact that a distro is an agglomeration of independently released packages means that there will be breakages like the ones you describe, because every package has its own concept of stable release, development cycle, feature deprecation, old version support, and so on.