The main reason why MobileReader's tend to hang on to the 2.0.1 version is that in the newer versions, Adobe included the possibility for book sellers to use an updated version of the content server which will deliver books via a different DRM scheme (meaning it hasn't been hacked yet).
I don't think anyone's come across anyone using the new server, which is why the 3.0 and 4.0 versions still work with the DRM removal tools. But the potential is there with the newer versions, so people have been sticking with the 2.0.1 versions of Adobe Digital Editions. Took a bit of digging, but I found the old post where the potential DRM scheme was first mentioned:
https://www.mobileread.com/forums/sh...d.php?t=231939