No, I do not want to over generalize, which is what I felt ivymike was doing- I appreciate his posts and have come to expect more.
HM oils as a class are generally intended for engines with over 75K of service; most make no claims regarding extended drain and so increased lubricant durability is not a characteristic feature. Is there a misunderstanding of this product class?
Here are the claims for Valvoline MaxLife*:
Helps condition seals and prevent leaks
Helps reduce oil consumption
Helps reduce deposit formation
Helps provide easier cold starts
Is safe for new and rebuilt engines
Note that the first two may be directly related to seals, and most HM products will include similar claims. There are formulation strategies as well as accepted industry standard tests for seal swelling/shrinking, so that is a safe place to start to develop legitimate, customer differentiable benefits for a HM motor oil product.
On this forum we are not completely at the mercy of buzz words and advertising slogans because of the breadth of technical expertise of the membership. And accuracy should be a goal. ‘Snake oil’ is a pejorative term referring to a product that delivers no real benefit and may actually cause harm. That these products have technically differentiable performance and have found a place in the market appears to attest that they deliver a real consumer benefit for at least some portion of the market.
As for ZDDP, the MaxLife product claims API SJ service category, which allows higher phosphorus than the SL or SM oils. Whether this is of benefit to older engines is arguable (without any data) because the SL and SM specs still require passing tests for valve train wear in their engine sequences. Some newer engines also have more stringent cleanliness requirements due to higher-performance design than older engines. Although the current API and ILSAC categories are supposed to be backwards-serviceable, it is becoming more of a stretch as motor oils become more highly developed.
*BTW, I am in no way affiliated with Valvoline or its parent company