"What is there to improve for mouse movement? It either works as expected or it doesn't work as expected (laggy, slow response) in which case it's an ISSUE they FIXED, not an "improvement" they made."
A mouse either works or it doesn't. A functioning mouse can work, but not work as desired. Any efforts to make it work as desired is an improvement...it is what quality control is all about.
Using your logic, then what gives with the OS service packs? Aren't they already working, so why improve them. Bottom line: there is always room to make things better through improvement.