I think you're missing the point. If you're observed wearing a watch, it may not be an accurate indicator of puncuality. But, if you have a bare wrist, it might be a subliminal signal to an interviewer that you don't care what the time is. You may have a hockey sock full of electronic devices on your person that tell time - during an interview, the only one that would/should be visible, is a watch.
If a person is clearly the best candidate for a particular job, it's not likely to be a concern. But, if the competition is tight, it could come down to a little detail such as that.