Because a bad video card / drivers combinations can produce all kinds of weird artifacts when hardware mouse support is enabled. Roughly in order of "How much of a pain it is":
* The mouse cursor may not appear at all.
* The mouse cursor may appear, but visual artifacts occur when the mouse is moved (which may or may not have any relationship to where the mouse actually is)
* The mouse cursor may appear, but not change when it should (in response to what lies under the mouse, for example).
* The mouse cursor appears, and changes image correctly, but the "hotspot" (the spot where the ap