I think that they're showing "boxed" body components. Integral reinforcement as you said.
Like the rocker panels are one of the most important structural elements of the unibody. People often overlook that area when dealing with rust. The "frame rails" are just added stiffeners. They'll replace the stiffeners and leave the rusted out rocker panels.
So, when looking at the cowl, or any body area, look for those reinforced areas. But, I'm not a structural or automotive engineer, so don't put too much weight in to my words.
Somebody had a thread on the site where they really went deep in to how to reinforce the body. I think that they even built a framework to load the frame and measure deflection. It might be in an FAQ area, or might be found by a search.