Yeah my FPS is a bit lower on the maximum 1080P as well, but there are some settings that are clearly intended for the very highest end gaming rigs on that setting that impact performance more than they provide quality. I turned those off and the FPS jumped back up to 30. (It's my processor that's the bottleneck at this point.)
I suspect those high performance scores on Ivy Bridge systems using a hexacore CPU paired with a simple Intel HD GPU suggest that the ARR game engine is coded with the PS3 in mind since it too is reliant on using its cell processor to do most of the graphical heavy lifting. It should be good news for those with modern processors but not necessarily the strongest of graphics cards.