Oh, definetly, shadows and focus can fool our eyes into seeing depth in a 2 diminsional image. Both schools are correct too... but it comes down to what are you trying to accomplish and who are going to be viewing your images.
You can play with focus and lighting and background and props, etc., if you are going for something artsy. If you are trying to sell something, you want the object to be presented as accurately as possible and you want the person viewing to focus on what it is you are selling. That doesn't mean you can't be artsy as well as functional, but it takes a person that has this talent to be able to do that. I'm not that type of person, so I've always leaned more towards simple and plain so that what it was I was photographing was the key element. Sometimes I wish I could be more artsy though.
Mike