> An alternative is intentionally packaging releases into tiers (performance, stability, feature, etc) and sell them as such. That could quickly devolve into s

> An alternative is intentionally packaging releases into tiers (performance, stability, feature, etc) and sell them as such. That could quickly devolve into supporting a large number of distinct versions of the software, which would be difficult and costly. Nobody wants to do that. Not to mention that, if this versioned software is a platform (for example, WinXP and its service packs you mention), downstream vendors would also need to QA and support their software on all actively supported versions of said platform.