That the book didn't include battle damage was my biggest disappointment with it; all of the focus is on the same weathering techniques that you can get from books on weathering armor models.
One of the other things I noticed that got handwaved in the articles was the effect of size on the weathering. For example, if you're applying rust to a mecha, the size of the effect is going to vary considerably between a four-meter AMP suit from "Avatar", a 20-meter Gundam, and the 80-meter Gipsy Danger from "Pacific Rim", in the same way they'd change between a 1/35th and 1/72nd scale model. Similarly, environmental effects -- dirt, mud, and anything else kicked up from the ground -- wouldn't come up as far on taller mecha; an AMP suit might go into mud to its waist and splash mud over the canopy, but the same mud wouldn't reach the knees of a Gundam, and might not reach the top of Gipsy Danger's feet.
All of the weathering examples are very well done technically, as you'd expect from Mig Jimenez, but it feels as if all the articles stayed safely inside the 'comfort range' of techniques from armor modeling, where vehicles are all roughly the same size, so the weathering effects don't have to scale.