The iPhone was originally so ahead of the competition (well, so was the iPod I guess) that its features were the 'wow' factor. It was a sleek, well designed object but I think its functionality overshadowed its beauty. Now that other phones have similar features, the time is right for Apple to revamp the design for aesthetic/form-factor reasons. Think about it: lots of people on the subway with these gorgeous, scratch-proof, slightly retro-looking, ultra-crisp smartphones shimmering beneath layers of glass on both sides, vs. a whole motley crew of less beautiful Android models rarely seen together. Which phone will people want?
Also: they compared the new glass to sapphire crystal, which in my experience NEVER gets scratches (its on my wrist watch cover). Does anyone know enough about the hardness of this material Apple are using to assert how scratch-resistant they'll really be?