Remember, pushing does almost nothing to add shadow detail. What it does do is increase density and therefore contrast in the near shadows, midtones and highlights and therefore improve the appearance of the near shadows and midtones. The increase in density and contrast in the highlights degrades (at least slightly) the quality of the highlight reproduction.
When Kodak is recommending no change in development time, they are essentially saying that with a one-stop "push" increase in development time, the benefit achieved in the near-shadow and midtone areas is of less value than the detriment experienced in the highlights. No doubt that turns mostly on the fact that the film does an excellent job capturing detail in those near-shadow and midtone regions, even when under-exposed by a stop.