Wow -- the traffic that's happened while I'm away!
A few folks have hit on the real conclusion stress risers in a hard, non-fibrous material make for the weakest points during conditions of shock and vibration. This is a fact, whether considering a scribe line in a concrete driveway, a 0.1" crack in a percussionists 18" diameter cymbal, or serrations in a knife. Ever notice that when driveways are poured, seemingly insignificant cuts that are just a fraction of the total concrete thickness are put into the concrete before it dries? Those cuts create a sharp discontinuity in the concrete, thus introducing a stress riser to insure that when the ground shifts, the concrete breaks in a clean, controlled fashion. Drummers will tell you that they can play a crash cymbal for decades w/ no breakage, unless a latent defect introduces even the smallest micro-crack. That crack is, once again, a sharp discontinuity in the cymbal material, resulting in a stress riser. From there, the drummer is just a gig away from that cymbal being uselessly broken.
Its the same phenomenon with serrations (or any abrupt discontinuity in the material) in a knife blade, but to a vastly different degree relative to intended use. Many knife manufacturers craft serrations into their blades for the improved utility those serrations provide. These manufacturers know that under judicious, real life use, the shock and vibration in the knife will not cause failures and the user that preferred the serrations will benefit from the utility of that design feature. If the knife is abused with heavy, prolonged, metal-to-metal shock, the most significant stress riser, likely the serrations, will be where the knife would break.
If we could go back in time before Noss started his knife tests and grind serrations into all of the originally non-serrated knives subjected to mallet strikes, I would surmise that all of the knife test breakage results would mirror those of the GB and Project I. Does this say that serrations are bad? Your decision, based on your intended use. For me, I say no, just as I say that Ill enjoy the benefits of low road clearance on my sports sedan, knowing that its a feature that will probably cause operational failure if Im trying to cross a stream with the car.
The Green Beret and Project I were designed with the serrations being specific product requirements demanded by military professionals. Both knives have been successfully field tested by thousands in hard-use, mission-critical applications, with exceptional results reported.