From my perspective the challenge is, what happens if there is a critical bug found after 3 years and you're on the Apache version? Do they backport the fix (out of kindness)? I've jumped through many hoops in the past to pay for fixes to older open source systems - because the systems weren't properly updated - to get a patch, and it was never easy (and fixing this yourself is nearly impossible if the bug isn't obvious, and you don't want to break things in such a core technology).
I believe a section of the FAQ mentions that the previous versions (released under Apache) will no longer receive any updates and you're not allowed to integrate the changes to the newer versions into the older codebase.
