I think it's more the fact that in my experience, art subjects are graded on your ability to experiment with varying media, and extrapolate your ideas into new ones. That, and the whole "relate your work to that of other artists", which I am bad at.
So um if you can draw but you can't produce several hundred drawings a month and then bullshit about them enough to fill three sketchbooks, don't study art. A friend of mine got an A* in GCSE Art for painting stick men over a map of the London Underground, but he had some interesting things to say about it all. I usually come up with "I wanted to draw this so I did" and that's that.
@brandons48: Are you working from light to dark with your current drawing? Building up the contrast in layers as you go along?