Yes, you need robot makers.
But the whole point of automation is to reduce costs or increase productivity or quality.
If you robotize McDonalds, you're not going to increase the number of people who eat there ; that's pretty much determined by the size of the restaurant and the capacity of the kitchen. Quality is pretty much set by the quality of the ingredients, and is not the reason people eat in McDonalds.
The kitchen labour is flexible - McDonalds go to great pains to have people on contracts that mean they can have them work as little or as much as they need. So the thing they are making flex is labour, not production. Add robots, and you have less human labour. If you don't, there is no economic reason to do so - you don't need more production (or they would be having problems recruiting, not trying to keep their workforce lean).
If robots cost more to make and maintain than your human labour, you don't use them. Therefore robots mean fewer dollars in the pockets of human labour. It creates SOME jobs higher up the supply chain, sure, but not the kind of jobs that McDonalds kitchen labour can do - these guys are by and large, on the lower half of the bell curve for ability, as you point out. But if you need to spend more dollars on robots and engineers to handle them, you're doing it wrong. Therefore more money departs from the labour end of the economy (the customers of McDonalds) and into the pockets of the owners (the customers of 5 star restaurants).
Extend this to every low-skill employer and you have a vast underclass of unemployed people who i) need supporting ii) can no longer afford to buy goods and services that they previously would have afforded.
Lower demand means less economic activity which means more push to increase productivity and decrease labour.
Before long, robots are making the robots. The only guy with a job in robotics is the guy who maintains the robot maintaining robot. Sooner or later they realise that if they make another robot maintaining robot, they can make him redundant too.
At this point you can go one of two ways :
i) The 0.1% own all the robots and don't see why they should share their wealth. The remaining human population compete for an increasingly small pool of non-automatable jobs, the unemployed are herded into basic subsistence camps (by robot "peacekeepers").
ii) Everyone realises that the robots are made of materials from the Earth, and powered by energy from the Sun, that the Earth should be owned by all of us equally and that we should be striving for universal human happiness, and that if we cooperate we can all have a living standard that exceeds the definition of "comfortable" by some large margin, since all these robots made everything so gosh-darned productive