The problem is not the recievers. The real problem is the design of the play. The offense doesn't allow for things that will get a reciever open such as double moves, fakes, disquising where the ball will be thrown, etc. In that INT which Romo was throwing to Williams, he had completely beat his man with a double move and went straight downfield and was open. However, Romo threw it where the reciever was supposed to be.
Now I know the importance of running the correct route and making sure that your in chemistry with your QB. But when a play isn't changed up to the strength of a player, than you have a very vanilla, very predictable offense. This is exactly what the Cowboys is like. Predictable, vanilla and lacks flexibility and the abilty to make changes which benefits both QB and the reciever.