Certainly there will be specialized robots. Hell, we already have that with Roomba to a degree. However, I think the point you are missing is we are referring to general purpose robots where the system has the knowledge of all kinds of jobs.

For example, lets use domestic robots. If you take all the tasks associated with a home, you could specialize some of them but, if you wanted a general purpose that could handle it all, what better form than a human. Surely there will be adaptations with certain things removed with others added.

Under your scenario, depending upon what one's precise definition of a robot, we could be looking at higher numbers if we include specialized robots into the equation.

We will see how the development proceeds the next 10 years.