linux isn't targeting a single customer nor a single process. it is flexible and always evolving, unlike industrial process where you design something once and you're done with it. there's no comparison between the two, they are completely different domains.

just because linus doesn't have any specs to show you, doesn't mean linus doesn't have a plan. don't confuse the two.

even specs don't help produce reliable code in the industrial process domains. what counts there is good peer review and testing to the limits of your sanity. choosing a good language can help too.