In the words of the technical director behind Frostbite, the underlying engine for Battlefield 4, "We use DX11.1, there are some optimizations in it (constant buffer offsets, dynamic buffers as SRVs) that we got in to the the API that improves CPU performance in our rendering when one runs with DX11.1." This could give Radeon HD 7000 series GPUs an edge over their GeForce competitors. GPUs based on NVIDIA's "Kepler" micro-architecture don't fully support DirectX 11.1. Incidentally, Battlefield 4 was just bagged and tagged by AMD for its future "Never Settle" bundle.
Yes, I know that we have the news about the bf4 will support dx11.1 but this is a different subject.