Wow! I'm not a fan of Apple by any stretch of the imagination, but what an amazing job integrating all of the components and sub-systems in a light, compact form-factor. Truly impressive engineering. But, I like to give credit where credit is due and am really impressed by all the Chinese workers putting in 18-hour days cranking these things out by the millions. Their effort and attention to detail is outstanding.
You haven't seen your cordless phone battery lately have you?.
Most cellphones batteries may apear to have a good energy density from their reduced footprint & with 5Hr talk time, but not much better than most tablets.