You do realise that trademark protection exists with or without registration, right? Registration confers additional rights to your trademark, but even without registration, other businesses are not permitted to imitate you... Therefore, even without taking the step of registration, there is still formal intellectual property protection, which the GP is correct in saying that businesses that trade on their reputation rely on.
Yes, I've take several IP law courses. The problem with this logic in my mind, however, is that there is no way to directly trace the effects of formal protection to the empirical outcomes we witness in the world.
E.g., you could say the same exact thing about copyright. Copyright applies whether you register or not, but registration confers important advantages. Does this mean that everyone who creates anything copyrightable "relies" on copyright?
If a business wasn't able to have exclusivity over the name tied to their reputation, such a reputation would be very difficult to foster in the first place.
That's obviously true, but it assumes that trademark law is the only thing providing exclusivity. Or to put it another way, it assumes that every competitor is waiting to jump in and rip off someone's name and image, and the only thing preventing them is trademark law. I don't buy into that logic for tangible property: I don't assume that everyone is planning to steal from me, and the only thing restraining them is the law.