I'm surprised the article didn't mention bunnyhopping or other kinds of physics exploitation-based gameplay. It could also have talked about games like Rocket League which rely on completely impossible physics to make a fun game.
Movement systems were programmed independently to collision. Physics is mostly used for collision in a standard first person shooter. You can use it for 6dof space or underwater vehicles.
as far as I remember, it was to do with jumping sideways being a lot faster than other movement, but I can't imagine why you'd program that in?
- if "forward" key held down, add unit motion vector to position
- if "left" key held down, rotate motion vector to left and add it to the position
In that case, you've added two copies of the vector at 90 degrees to each other, and the player moves by sqrt(2) times the normal speed.