Note: Shimano 8- and 9- and 10-speed cassettes/hubs are fully interchangeable for wheels with steel Freehub bodies.
The only parts that are different in any important way between the 8- and 9- and 10-speed systems are the shift control levers.
The 2004 Dura-Ace hub has an aluminum Freehub body, so it only works with 10 speed cassettes.
This is not true of the Ultegra 10 hub.
The Ultegra 10 will take any standard Shimano cassette.
Dura-Ace 10 cassettes have titanium sprockets from 18 teeth and larger.
10-speed cassettes have a recess built into the back of the big spider module, allowing them to fit farther onto the Freehub body than older cassettes. This limits the possiblities of customizing the ratios, because you can't install a flat sprocket behind the spider module...you run out of clearance at the other end if you try.