Additive guy is correct. But I think dropitby was trying to say that the need to fortify a good oil further shouldn't exist. But then again even good oils don't perform well in every application or operating condition and additives are often the best solution.
I know that most wynn's additives contain friction proofing which fortify's beyond any additive included in regular API requirments by coating the internal components with a teflon like seal.
The problem with oil is that there is generally no immediate evidence (except for SAE variances or oil change discoloration) that it is performing better unless an SOS is performed. But I can vouch from experience the long term benefits of additive overtreats - either in the oil itself or from a bottle addittive like wynns.