What did they do feature-wise in newer versions that makes the old versions desirable to some people, to the point that a user would prefer to upgrade them rather than upgrade to the newest version? It's not about system compatibility: the 2.x line supports Windows all the way back to Windows 7.
I'm content to dig into the docs but I was wondering about people's personal experiences with it. One hint in the release notes is that some, but not all, old plugins work in the new version...