I’ve worked on both sides of the aisle, heavy on design and heavy on coding. If you notice in the after picture, all the icons and numbers are bigger or easier to read, and that’s really the crux of design. Content is king, if you’re not presenting the content in an easy to understand way you’re hurting yourself, and if it’s not easy to see you’re killing yourself.
I bet the before photo’s web 2.0 glow on the buttons is making the white numbers difficult to read, especially with glare. In the after there’s more contrast and it’s easier to see. Also, as others mentioned, it looks like he snapped to the pixel grid on one and not the other. With the snap none of the pixels take up an unrenderable half-pixel on the screen, so everything is displayed the way it was intended instead of on the whim of the graphics processor.