If I decline, I decline without a response. I'm a rude, obnoxious SOB, and I ain't about to change for anyone. However, I don't have to decline anymore, cuz NO ONE INVITES ME!!!
I think the point that was originally brought up though is that the invite was sent out, and not accepted OR declined. Nothing! Nada!
My response to that would be that perhaps the person is not up to playing at that particular time, but would like to hang onto the invite to accept a day or 2 later. I have done that at times.