The 2012 iPad has 42.5-watt battery compared to the iPad 2's battery coming in at a mere 25-watt. And yet, the new iPad manages only to meet the battery life of the iPad 2 - coming on at 10 hours of use on WiFi and the same cellular use at around 9 hours. The main difference here is the vastly improved Retina Display on the 2012 iPad versus the iPad 2.
The question is just how much of a big deal is LTE use for the new iPad versus the 3G in the iPad 2? With both coming in at 9-hours, you have to assume the power consumption are the same. And the only other factor that might impact the extra power use would be the new display.
And you have to marvel at Apple's engineering for managing to fit such a bigger battery inside the 2012 iPad. You can almost correctly say that the iPad is a battery that happens to have a dense multi-touch screen that runs iOS.
A further thought along this line is that the Retina Display is not very efficient. We already know the LTE chip inside the iPad draws as much power as the 3G chip inside the iPad 2, hence, the display probably could use a little more work. More likely, we'll see some kind of improvement with the 2013 iPad's display.
Once Apple's engineers manage to smooth out the power issue of the 2013 display, we should see Apple continue its march towards a thinner iPad along with improved battery life.