I think its time we went beyond glass, yes there are many variants and Corning make the current glass panels in the iPhone 4 if correct.
Now we should be using Sapphire Crystal, instead of glass. Its stronger, almost scratch proof, does not have issues with fingerprints, and therefore no need for Apple's oleo phobic coating to reduce fingerprints (which I am sure wears off over time just like any coating which is not sealed inside the glass, but layered on top), no shattering of screen, no need for screen protectors (you can still buy them and use them).
I am not aware if Sapphire Crystal can be used on curved surfaces, but if it can I think it would match the iWatch perfectly as well. Time to move to Sapphire Crystal I say 🙂