I've never heard anybody complain about volume. Just width/height.
I mean, isn't everyone here on HN always making fun of Apple's supposedly unnecessary obsession with thinness? Now it's a teensy bit thicker.
You've never heard of people complaining about how "big" phones are, and wishing for a "smaller" phone? How would you measure "big" and "smaller" other than volume?
The 2D surface area, which affects holding and pocketing, is 13% larger.
Weight also matters.
I honestly still prefer the form factor of the iPhone 3GS. (I have an old one in a drawer for comparison.) 4.8 ounces, 4.5 x 2.4 x 0.48 with a rounded back. The thickness wasn't a problem.