Perspective? That doesn't even begin to explain it. That picture looked odd to me before, but after looking at the specs it simply can not happen. That sort of arrangement could distort the apparent difference in thickness and mask the difference in width. But it would exacerbate the difference in length.

You can't possibly put the Galaxy S3 in front of the iPhone and create that scene. That picture is a mess.

iPhone 4/4S: 115.2 x 58.6 x 9.3mm

Galaxy S3: 136.6 x 70.6 x 8.6mm