Don't think there's an issue with people being moved on stalwarts or no providing those who replace them are as good and younger or better. This certainly wasn't the case after Munro was pushed out.
Dave is a well liked, good, hardworking player who sees to fit Hughes' 'gud honest laddie' to a T. He seems to want to stay but yet he's unwanted dispite Hughes moaning about how hard it is to get players up here. Unless Dave is demanding a silly amount of money (which is unlikely as he's not been made any offer it seems) I can only assume it's a personal issue/dislike the manager has for the player.
Sad state of affairs.