The reason for DICE delaying the PC release of Mirror's Edge may be a little clearer.
DICE are retooling the PC version with enhanced graphics and - video card permitting - the NVIDIA PhysX engine to allow more accurate physics modelling of the virtual cityscape and the many, many things that can realistically fall off it.
As you can see in the trailer (after the jump) it does look rather lovely. Suitably equipped PC owners will be able to realistically fall off things in January.
DICE Puts Faith in NVIDIA PhysX Technology for Mirror's Edge [Game Info Wire]