Guild Wars 2

Most people probably don’t care because they think zoom is placed well on the mouse wheel, and most of the people who actually care create a profile in their mouse software to rebind it, which leaves just a small minority in need of this feature.

In addition to what Iruwen has said, you should also consider that the mouse wheel is used for other things too, like scrolling through UI screens and the chat window. The way the game interface was designed, the mouse wheel is hard coded to multiple specific functions, so allowing you to bind them to other functions could get complex, because you would either have to no longer be able to use it for default functions like scrolling, or they would need to make it so that any bindable functions are superseded by default functions except zooming. This could be possible, but I doubt there is enough demand for it that ANet will spend the time.

Anyway, as Iruwen said, you can try to use your mouse software to rebind the mousewheel functions. If that doesn’t work, or if you don’t have mouse control software that will do it, you could try using Auto HotKey to intercept the mousewheel signals and replace them with something else that is bindable. You can get Auto HotKey at http://www.autohotkey.com/.