Demerit of declaring static method in AbstractFactory

The disadvantage of declaring static method in Factory class, according to Head First Design Pattern - "you can't subclass and change the behavior of getPizza method". getPizza method is used by Factory class to decide which type of object to return. If I understand correctly, my class is

    public class PizzaFactory {
        public static Pizza getPizza(String type) {
            if (type.equals("cheese"))
                return new CheesePizza();
            else if (type.equalsIgnoreCase("thisCrust"))
                return new ThinCrustPizza();
            return null;
        }
    }

Even though the method is static I can always create a subclass like -

public class DelhiPizzaFactory extends PizzaFactory {
    public static Pizza getPizza(String type) {
        if (type.equals("cheese"))
            return new CheesePizza();
        else if (type.equalsIgnoreCase("thisCrust"))
            return new ThinCrustPizza();
        return null;
    }
}

I can use both the superclass and subclass interchangeably.

public class PizzaStore {

    Pizza pizza;

    public void orderPizza(String type) {
        pizza = DelhiPizzaFactory.getPizza(type);
        pizza.prepare();
        pizza.bake();
    }
}

So what is the disadvantage?