I've had my license for 2 years now. I've never ever had to look to the middle of my car to see if I'd run off the road, only when doing 3-point turns or when parking, at which point the speedometer doesn't matter. Try driving in a straigt line when looking at your radio or navigation in the middle of your car. You'll slowly drift towards the right (or left if you have a the steering wheel on the right), especially if you do it for more than a second (which you will do if you try to get your speed right).