Why Quake 1 & 2 invoke mouse acceleration

I discovered that both Quake 1 & 2 invoke SystemParametersInfo in IN_ActivateMouse with the third variable being {0,0,1}. The 1 activates mouse acceleration. Quake 3 doesn't invoke SystemParametersInfo in IN_ActivateWin32Mouse, so it uses whatever you have set for mouse accel (what Microsoft calls 'enhanced pointer precision'.) Well you can morph the mouse acceleration curve into a linear response line by editing the registry such as the mouse-acceleration-fix by MarkC. So if an application activates mouse acceleration it will still be linear.