The main reason is that when I'm in a dark tunnel, sometimes I still want to see it dark, same with night (specially if I want to see something in color, or I got a cool torch I'm trying out). During a new moon when it's really dark, I should be able to use ears, but I should also be able to look around too, with my own eyes (with my own camera angle at least).
Or it could be like radar, when you fight in enemy, or when Turner hears an enemy, his ears perk up. They'll point in the direction of the sound, however they can. If it's from the front, they'll twitch and then point forward, they'll lean and point towards things that are coming from the side, sounds from behind- they'll get real low and cave in for incoming sound to pass through, just like real ears (dog ears at least, mine don't do that yet...). I use this alot in those Vigilante games, you'll get like an auto aiming turret and you follow where it's pointing to, to reach whatever enemy it's aiming at. Cept ears would make more sense because he'd hear them.
I want to add more about that picture in a picture for smell. I'll stop for now though.
You have to find some use for that scroll wheel, maybe something different from zooming in (zooming would be cool, I need a mug-shot for Turner) and switching weapons.