It's intended as recreation, yeah, but to me watching that video was like watching someone carry large rocks without aid of a wheelbarrow.
Or like digging a large ditch without aid of a backhoe.
To me there is a clear hierarchy or graduation of puzzles. Metaphorically:
1. Ditch digging by hand.
2. Planning efficient ditch layouts to be dug by machines.
3. Designing new and better ditch digging machines.
- - - -
1. Solving Sudoku puzzles.
2. Designing new Sudoku puzzles (with additional constraints even.)
3. Designing e.g. CLP(FD) programs to solve all sudoku puzzles everywhere.
- - - -
What I'm saying is, Why don't people move up that hierarchy? Why is level 1 so fascinating to people?
I believe that anyone who can solve sudoku can program a computer, but they don't. Why not?
You can have fun at all those levels, jumping back and forth between them at your leisure. Just because you can program a computer to solve a sudoku doesn't mean that you can't enjoy solving one by hand from time to time. Digging a ditch can be fun too, as long as you don't have to do it all the time.
I wouldn't think Sudoku is machine work. Yes, a machine can solve it, but it's not intended to be machine work.