The iPhone4 is Corning Gorilla Glass... both the screen and the back glass. Apple and Corning have both stated that it is. . . Steve Jobs stated it as a fact in the introduction of the iPhone4. The glass is made by several manufacturers under license from Corning.
As for your link to the scratched iPhone: Again, you find the stuff from the fringes and post it as fact. I have many friend with iPhone4s and none of them, including myself, have succeeded in scratching our phones.
Great, I’m sure you can provide a reference? I haven’t been able to find anything other than Apple saying it’s an aluminosilicate screen...