Until very recently we did not have stable branches to which we backported anything. This was mainly due to lack of dev manpower. With the last big release (1.8) we decided to try and maintain a branch to backport things to, which we named 1.8.x. The general notion here is to backport all non-trivial fixes that can easily be backported, esp if they are significant such as is always the case with security related bugs. Though that is the goal, we have only backported a limited number of things so far, and could do better. Then again, there are many other things we ought to do better, and only so little time people have.
Personally I've been wanting to do a new minor release ever since the fix you are talking about, though have not found the time so far. We need more devs! :)