One other difference between the AVR-2310 and the 2311 is the video processing chips used. The 2310 uses Anchor Bay's ABT2010 chip, which has been around for a few years. The 2311 uses the ABT2015 chip, which was just released this year. There is a good comparison of the chips offered by Anchor Bay, but AVS won't let me post a link yet because I'm such a newbie.
The comparison table doesn't reveal many differences between the 2010 and the 2015, but if you check out their individual pages, it's clear that the 2015 has more features.
The problem is that Denon doesn't come right out and announce the specific features they have or haven't enabled, so it shouldn't be assumed that the AVR-2311 has all the features that the 2015 offers. In fact, at this point, I've had a hard time finding the differences in the video processing offered by the AVR-2310's ABT2010 and the AVR-2311's ABT2015.
If anyone happens to see an advantage in the 2311 over the 2310 in the context of video processing, I'd love to hear about it!