If a graph has a spike, that implies "high rate of change". How high the peak is is all that really counts, as the body produces insulin in accordance to how high your blood sugar currently is - it has no way of knowing what the area under the curve will be in the end. And inevitably it overproduces if the peak is too high, since we are not evolved to deal with modern high GI carbs.
"How high the peak is is all that really counts".
You severely underestimate the bodies predictive capability. There are 21+ pathways feeding into the insulin response system, all of them trying to prepare the internal system to get rid of glucose. Thought, taste, smell etc all contribute to our predictive capability.
The point is that the body tries to predict the amount of glucose ingested to minimise peaks. A long term marker of the bodies success at this is hba1c.
I'd love to see a reference for your last claim. Surely the mechanism of fat storage in periods of high sugar availability would be a desirable trait?
We know the body treats glucose in the bloodstream like a poison in the sense that it tries it's damnedest to get it out. Interesting articles:
http://www.phlaunt.com/diabetes/14045678.php
http://darwinstable.wordpress.com/tag/glucose/