I get the same effect by clicking on the scroll wheel on my Logitech (Cordless) TrackMan Wheel, then using the trackball to scroll around (dunno if Microsoft mice/trackballs offer the same deal; it's been forever since I used one). Also, for those times when precision scrolling (up/down only) is required, the wheel provides a tactile response. Somehow, I don't think Apple can offer the same combination with Mighty Mouse, but if they are, all the more power to them.
Yes, this is a feature of the operating system, not the trackball, so it's not just your Logitech that does this. But you don't get "the same effect", you get a better effect. By default, clicking the middle button (which is basically what the scroll click is) causes a reference point to appear at the cursor's current location, then scrolls in the direction the cursor is moved to. So let's say you want to scroll slowly through a document. Middle-click, then move the cursor down slightly, then stop. The document will scroll by and will keep on scrolling by. If you want to scroll faster, move the cursor down a little bit, and if you want to scroll slower, move it up a little bit. Good luck replicating the effect with a scroll ball like Apple's.