do long haired girls hold their hair behind their ears before they bob for apples?
maybe cats evolved from having big ears and even though they now have smaller ones, this quirky behaviour is a remnant of behaviour of old when they had to hold them back when leaning forward to to prevent dipping them in their chosen brew
of course using occams razor, the reason could be as simple as the notion that it positions its ears in a way where he can hear the most. Cats ears are obviously more mobile than ours as you have observed, so they work like a satellite dish...swivel swivel swivel until they get the best signal
from this picture we can see that hearing is a pretty important tool for cats, this one grew two sets
My mum's cat did it when he was a kitten was so cute to watch. Cat't wait to see him at the end of this month now he's a big cat. Think it is just a reflex thing.