You're not thick headed at all - in fact, you're right.
It really IS calories in versus calories out and you indeed burn more total calories at a higher intensity of exercise than lower. Sure, you burn a higher
percentage of calories from fat at low intensities but you burn more
total calories at higher intensities. Did you know that you actually burn the highest percent of calories from fat when you're lying in bed? Even so, I don't think it's going to do much for anyone's weight loss.
So no, you're not going to burn more fat by slowing down on the elliptical. The whole idea of a 'fat-burning zone' is a myth.
'Anaerobic' simply means that you're working above 90% of your max heart rate and that's very difficult to do for a sustained period of time, like more than a minute or two. For our purposes - fat loss - keep your heart rate somewhere around 70 and 85% of your maximum heart rate. The higher the intensity, the higher your heart rate and the more calories you're burning.