The whole point of washout is to provide roll control at speeds around stall speed. Not all airplanes have this which is why it's still a good practice to teach, regardless of being able to demonstrate it!
Minor qualification - maintaining reasonable roll control is a Design Standard requirement and will apply to all conforming Types other than those of ancient design.
See, for instance,
FAR 23.201(d).
If you play in the FAA website and have a look at superseded Regs .. you'll find this goes back a long ways ...