I can definitely see the effect which the OP is describing in these two images.
And it is more or less an optical illusion, but it's an optical illusion that you would only perceive in a 2d image.
Because the image is in 2d, there is no actual depth perception, so our brains try and estimate depth and relative size.
What's making it look "thicker" in the images is the highlights and shadows created by a taper under lights. You would quite easily be able to perceive actual depth and determine it was thinner in person, but in a picture, with the right lighting and angle, the iPad 2 can be PERCEIVED as being thicker...