The "resolution" of the scroll wheel of your Logitech is not high enough to produce the smoothness of scroll you're looking for. Your trackpad senses scroll movement much more accurately than your mouse.
To illustrate, scroll very slowly with your trackpad, and then scroll very slowly with your mouse. You'll see the page jump after a certain point with the mouse. That will show the difference between what the mouse can see and what the trackpad sees in terms of movement. That's either a hardware limitation or a driver setting. If you can't adjust this behavior with the Logitech drivers (assuming you use them, I know I don't) then you're stuck.