As mentioned before, there are no unique units in the Civ 4 sense. Japanese Samurai Knights are exactly the same as regular knights, except in name and graphic. The only reason why Samurai Knights have +1 attack over regular knights is because of a specific Trait the Japanese get, it's not an inherent bonus like a Civ 4 UU.
I guess the developers believed China to be powerful enough, without the need for a bonus to a particular unit type.