This isn't true. You can one-hand use the watch if you use your nose to touch the display.
How do you interact with the AW if you are holding a cup of coffee?
I can see lots of people spilling their coffee during the learning phase when they tilt their wrist to see a new notification. The next challenge (after you learn to hold the coffee cup in your non-watch hand), is how do you hit the button or screen with the hand holding the coffee cup?