I can't agree that "Roger" or "Wilco", is sufficient as a replacement for a full route clearance readback. Too many times here, the yank pilots have said "roger" or "wilco" and on being pressed for a readback it becomes apparent that they were going to fly a different route than the one given too them. Hence the need for a readback. The American pilots are the least likely to readback, and the most likely to not adhere to the clearance recieved, recipe for disaster.