Zinc and other nutrients are NOT stripped out when extract is made. In fact, it is the exact opposite that is true. These nutrients are concentrated. So if you then add water on top of it that contains more salts and impurities, you end up with perhaps twice as much as you would for all-grain brewing.
The point that I think Tom might have been trying to make is that water is always low on zinc, which has been proven important for yeast health. So that's why some people add yeast nutrients or shave a teeny tiny bit of a zinc tablet into their raw beer to help the yeast with respect to zinc and other unidentified essential nutrients that might be important for yeast health.