Yeah but it doesn't take as many;
Once your design team of say 10 designs The Ditch Digger 2016, They are no longer needed. In my field the either get laid off or they were contract engineers.
The factory that makes The Ditch Digger 2016 Has robotic maneuvering are, a robotic weld line etc.
You have a staff of 5 guys that know (P)rogrammable (L)ogic (C)ontrolers, and other variouse controls.
A staff of 5 for mechanical issues.
and 1 or 2 facility engineers.
Anything else is has outside help called in.
That's it for the factory. Now this same factory had maybe 20-50 people work assembly
10-20 welders. 10 inspectors, plus the crew above.
40- 80 people just lost their jobs because of the robots.
You're looking at it technologically. So, yes, digging ditches may be obsolete, but creating the machine to dig those ditches will take people.