We are comparing devices with relatively large screens and a lot of exposed glass. That's the relevant comparison.
Not really because iPhone is built differently with glass on back. The exposed edge is definitely a weakness of iPhone. Hopefully this is something that'll be fixed with the new metal back and a new construction.
How easy something shatters is probably one of the most practical measures of a better build other than wear and tear effect. And I don't think either the Iphone or the S3 is going to look much worst during a normal usage cycle of 2 years or so.
As bad as glass is for shattering, one thing it is good at is minimizing effect of wear and tear . Compared to plastic, it's much better at resisting scratches. My Galaxy S from 2010 looks much more worn compared to my friends' iPhone 4 bought in the same year. That's probably at least a part of the reason as to why Apple chose it in the first place.