I wish smooth scrolling could be enabled EVERYWHERE, sadly smooth scrolling can not be enabled for mouse wheels because they have "jumps" whereas the scroll input from a touchpad is precise enough to register pixel-for-pixel motion.

To test this out, fire up a terminal and run

xev

Then place the cursor in the window and scroll up and down. You will notice that the key (button 4 and 5) registers output continually as long as you move your fingers. Now scroll with the click-wheel. It will only register once per mouse-wheel click.

Some mouse-wheels do not have distinct "jumps" when rolling but I'll bet that the hardware reads the distance travelled by the roller, and sends jumps just like other mice to insure hardware compatibility.