One of the target goals of the "old" versions of redactor was/is the backwards compatibility with browsers. Those scripts that use the newer/later versions of Redactor have eliminated access to posting to those forum users that are still stuck on said older browsers.
I have seen some tout the WBB "they have the newer Redactor" horn.. but at the same time, those people that are still stuck on Windows XP and older browsers (and yes, there are still many of them) cannot participate due to the newer Redactor lack of backwards compatibility (again, from indicators I have read).
There is a finely balanced line of "gotta have the latest/greatest" craze, and making the site available to the widest audience. Some will say "who cares" about the XP crowd, that they "should get with the modern times"... but fail to realize, not everyone necessarily has the funds to and some access the "interwebz" from their work as they don't have access from the house and many businesses are STILL stuck on Windows XP.
But, aside from that, as @Chris D indicated, a new editor is being implemented for the XF2 line.