Actually, the D-A pedal adds an outboard needle bearing to the 2 ball bearings found in the Ultegra pedal. The needle bearing adds additional load carrying capacity and durability to the construction. IMO, the extra cost of the D-A pedal is merited.
I'm using a pair of PD-6800 Ultegra carbon pedals on a winter beater right now and they are impressive in their construction, materials and finish. Entry is easy, but the release is a little noisy and not as smooth as my Campy pedals, but overall I think they're a very good pedal.