Every year when Cs-cart launches its updates I lose money, because Cs-cart does not have retro compatibility, they really should solve this and think more about their clients, every year I have to pay a certain company to reconnect a module that has cost a lot of money to integrate.
Good luck wi that one :)
Most addons done properly are compatible with updates. There are times (like when they release things like new checkout) that things to to hell. But I have many addons that integrate with outside services or extend admin functionality that move just fine from version to version as they make changes.
However, they could make life easier sometimes by preserving deprecated functions by simply having the old version act on some subset of the new (assuming deprecation was the result of adding functionality).
But when you do things like add variations and new checkouts to "minor revisions" you're going to have problems.
Question? are Magento and the like retro compatible
No idea on them specifically.
Most platform providers deprecate functionality (or extend it to the point where prior means can't support the new). However, most do this by deprecating major versions (like 4.x to 5.x). Cs-cart is one of the only platforms I work with that deprecate functionality in minor releases (I.e. going from 4.9 to 4.10) without providing backward compatibility to support 3rd party addons. This causes problems for addon developers who don't expect the rug pulled out from under them for a minor release.
Major versions (4.x, 5.x) are expected to be incompatible with each other.
Minor versions should maintain functional compatibility even as new functionality is added
Defect correction versions (4.11.3, 4.11.4) should NEVER impact any existing functionality or add new. It should correct defects only
Cs-cart has their own definition of things. But taking months to respond to bug reports and then not seeing those bugs released for even more months causes frustration among the user base.