The only reason it's a tenth of a millimeter thinner is because it has a lower-resolution screen. It's actually a good bit thicker than the normal-screen iPad 2. And it'll feel even thicker in your hands because of the squared edges (necessary to put all those ports in it).
The battery comparison is interesting, 31.5 vs. 42.5 W-h. Apple uses that larger battery to drive the high-resolution display, so battery life may be about equal. Apple has set the 10-hour standard, and nobody wants to fall below that.
Well, the surface has microSD, USB 2.0, Micro HD Video, plus 2×2 MIMO antennae, (none of which the iPad has), which should have added up to make it a bit thicker, instead the RT surface is actually thinner than the iPad.
As for the screen, the Surface has a cleartype HD screen screen (that measures 10.6 inches diagonally, compared to 9.7 inches for the iPad), that comes in the 16:9 aspect ratio, which is more suited to watching video in the widescreen format, compared to an aspect ratio of only 4:3 for the iPad.