I think this sort of thing comes up because of peoples conceived notion of what an "Aerobatic" is, everyone thinks of it as a manoeuvre specifically used in an "Air Show", but CAR 1988 (Correct me if I'm wrong) defines it as:
"… manoeuvres intentionally performed by an aircraft involving an abrupt change in its altitude, an abnormal attitude, or an abnormal variation in speed."
Now a stall is a manoeuvre that is performed intentionally and (usually) involves and abrupt change in attitude and/or possibly altitude, therefore it could certainly be classified as an "Aerobatic manoeuvre" therefore requiring the 3000ft.
But honestly that's only if you're splitting hairs and looking for a way to really try to justify the 3000ft recovering altitude, me personally I just think it's a good idea and don't see why not unless you're really worried about the extra few minutes to get to 3000ft in which case stop being so damned stingy!
I guess really everyone once upon a time thought "Well, if 3000ft is good enough for aerobatics it should be good enough for stalls then, let's go with that!" and so it became an un-written rule
