[nugga]

The way I could try to make sense of it is, something is being moved from outside so pushing the mouse forward means look down. Flight sims, joystick, 2d plane, ...stuff.

[AnIdiotOnTheNet]

By that reasoning pushing the mouse right should rotate the view left.

[petepete]

If you were holding a gun with two hands (and you're right-handed), you'd lift your right hand up to aim down.