I suspect it's so that applications and macro buttons on mice can send keyboard shortcuts without the risk of their keyboard input interfering with the user's keyboard or vice versa. It may also help in cases where there are multiple keyboards, one of which has something on it sending unwanted keystrokes, as any modifiers held down wouldn't affect input on the other keyboard. But it should be a configurable option for exactly this kind of reason. Anyway, glad this worked for you.
