I'm not sure the wheel was ever actually invented (where's the patent?
). For the rest ... I don't doubt the skills that many people have, but there are assumptions being made that may or may not bear out, depending on the catastrophe. Just what percentage of the population have the knowledge to build such things as aircraft, even on found materials? What percentage of the population do we expect to survive the catastrophe? How does the maths pan out? Let's say that a few do survive. Fine. For the day, the week, the month, the year after the catastrophe it may indeed be possible to do many things based on found materials, but keeping going in the long term is a different proposition, especially with a limited population. Creating a manufacturing infrastructure required for the long term is not an insignificant detail. If you keep relying only on found materials then the story told in many books of a slow decline of civilisation begins to look realistic.