In case you didn't know:
You can hold the Ctrl key pressed and use the mouse wheel to zoom.
Furthermore, you can hold the Shift key (or Alt - I don't remember).
The one combination is for vertical zoom, the other one for horizontal.
If you dislike this, there are surely 3rd party tools which can change the mouse wheel funtionality.
So when you use just the mouse wheel, it would be the same as Ctrl+mouse wheel.