There's some truth in all the posts above, I believe.
After much reading , I'm convinced that after much testing , the engineers (I'm using this term in a positive light) found that the 1LE handled the best with the current tire and wheel setup.
While the wider 305 rear tires would ultimately give the rear end more grip, they found that the stretched 285 rear tires, near the limit, allowed the 1LE to rotate slightly better in the turns with more nuetral handling, making it faster and more fun. If you can get a car to rotate in the turn, you can get back on the gas sooner than if the car is pushing. Of course, too much rotation--loose as hell--is slower too. If anything, the 1LE is balanced.
On the ZL1, the wider rear tire tires are necessary because of the extra weight and especially the extra power. Powah!!