To kind of get back to some of the original points, we have to remember WHO the clients of FICO are. The clients are the lenders. They have decided what sort of data that they want to see, so they are the ones who make the rules.
Also, I recently (up until 3/3/08) had a 768 EQ FICO WITHOUT any open revolving credit. I misjudged when HSBC would report and my score tanked. I have corrected the problem (and play the game now), in order to get my scores back to the high achiever range.
The other reason why the FICO model gives more credit to revolving debt is because they should. It's unsecured and therefore the most risky. Why shouldn't there be a greater risk/reward applied here?
Speaking as a former banker (commercial and retail), FICO is but only one of the factors considered in giving someone credit. I have turned down people in the high 700s and given people loans in the 500s. The "lenders" that give such weight to FICO are the ones taking the greatest risk (the CCCs).