From USEF: "Impulsion is the term used to describe the transmission of an eager and energetic, yet controlled propulsive energy generated from the hindquarters into the athletic movement of the horse. Its ultimate expression can be shown only through the horse’s soft and swinging back to be guided by a gentle contact with the rider’s hand."
Mentions nothing about whether or not said gait where impulsion exists must also have a moment of suspension. It is simply the feeling that you can halt or do an extended trot at your whim and the horse will be responsive, related to submission.
They say money doesn't buy happiness -- well happiness doesn't buy horses!