I wonder what you wonder about.
What did you think, do, the developers who do the rt-kernel patches does ? it is just to get a extension on the kernel name?
Well, the rt-kernel patches allow priority's for user space tasks, which aren't allowed by "normal" non PREEMPT kernel, and exactly that is, what we, as pro audio users been after. While in early day's of the rt-project, a lot of issues appears when user space could use though high priority's, this day's nearly all culprits been resolved. a lot work has been put into the kernel scheduler, to make all this work smooth.
But just that most of this patches been accepted in upstream, didn't mean that they are switched on by default. At least, debian, for example, is in use on servers much more then on desktop systems, and imagine yourself, how many of this desktop systems been meant to be used as "pro audio system".
So, what did that mean? You need to be aware that you've to sail your ship always a bit outside of the main floor. Otherwise you end up with a "perfect server system".
On the road again.