Chip prices change a lot depending on who you are (what you can negotiate and how much you want to buy). Apple is in a very special position as they have few products and a tendency to buy a part of their suppliers machines in exchange for guaranteed shipments and lower prices. The isupply table
http://www.isuppli.com/Teardowns/News/Pages/iPhone-4-Carries... shows pretty different prices even for Apples own A4 which should have a flat factory cost. As for the mechanical components, I guess that the 10.80 figure is a decent guesstimate which could be off by +/- 50%.