Tightening the tire/wheel arch gap improves aerodynamics as well.
MaxMatt: the first two links you provided didn't work for me, so I don't really know what the examples were meant to show.
As for wheel arch design for best aero - a minimal tire gap, is best, plus adding a radius to the aft edge to permit air exiting the arch to make a clean transition to the vehicle side.
EG see:
60+ Vehicle modifications for better fuel economy - EcoModder.com
Low Cd production vehicles that took pains specifically to shape the wheel arches include GM's EV1, Solectria Sunrise (pictured), Honda Insight (gen 1)...
Toyota mentioned tweaking the wheel arch liner on the new gen 3 Prius, but I'm not sure if it's to address the same thing.