It was a choice for the role. That's what he said in an interview at least.
That said, he does "hunch" but not when he hangs with tall friends.
When you see him a pack of swedes he's chin back and standing straight.
He should probably move back to sweden for the sake of his spine
http://bit.ly/Ash-vs-The-Evil-Dead

Because he's so tall he's always looking down towards people when he's talking to or listen to them. So now he is a hunch back. If you look at him from the side he's very head forward.