That's a good point. Robotics itself is an 'umbrella' category that covers so many different types of engineering.
Generally speaking robotics could be considered as bringing together electronics, mechanics and software(but of course all of those are not actually necessary for something to be considered a robot).
But if we were to just consider robots in a service sense(humanoid, wheeled, 'intelligent'), then there is no doubt that in the future more robots will be in service than there are humans(look at the automobile!).
Imagine if in an average home we were to have a humanoid, a smart vacuum cleaner, autonomous lawn mower, windows cleaner, cook,etc,etc,etc,etc...........!!!!