I think the bow arm is real important. But I also think it is interconected to other things including the release and alignment. If I keep those two aspects correct, then my bow arm stays put pretty good. But not the other way around. - That probably made no sense.
I constantly worry about a good release, which is important I might add. But I notice I will hit the mark more often when I concentrate on the bow arm.
Could it be that your release is better because of the lack of pressure (mentally) that you are putting towards it? That lack of pressure may lead to a more relaxed release.