The answer is quite simple actually. While checking out the hardware specs of the new iPad, we noticed that it comes with a 42.5Wh (watt-hour) battery. That is nearly twice the capacity of the iPad 2's battery cell, which is rated at 25Wh. However, as a battery's capacity increases, so does its physical size, which explains why the new iPad is slightly thicker than its predecessor. It has a thickness of 0.37 inches (9.4 mm), while the iPad 2 is only 0.34 inches (8.8 mm) thick. Still, not that big of a deal, in our opinion.
For everything related to Apple's new tablet, you can check out all our iPad 3 coverage.