I've worked on both avionics software and web software, and you're spot-on correct... the procedures and development styles are entirely different. Avionics development is laced with simple, easily-understandable coding techniques shrouded in requirements, verification, and paperwork. And yes, real people do sign off on things. Unlike in the web world, where you can whip out changes every day, it's not uncommon for there to be a delay of months (or even years) between writing a piece of code and deployment. We were working on software for the Boeing 787 about five years ago...
I work on SIL-4 systems for Rail (Transportation, not fancy web framework de-jour) applications .. the code I spent a year slaving over to ensure it is as bug-free as can possibly be rendered, won't ship to our customers until next year, and even they won't be deploying it in field for another year or so after they get done with their own tests. So, I'm looking at having to support that code from a year ago, 3 to 5 years from now.
