It also pays to remember just how recent most of what we call "technology" really is. You don't even have to go back 100 years to find a very different world. Sure there are people out there now that try to keep up some of the "old" skills, but what are the odds of those few surviving some apocalyptic event.
I find it slightly amusing reading the posts here that suggest that simply having access to the knowledge (even assuming you have the means to access it) will be enough. Anyone here care to reproduce the work of the Wright brothers from Wikipedia articles alone?
Apprenticeships can be long and hard for some of the skills (as opposed to raw knowledge) to be acquired, and they will be longer and harder if there are no masters to learn from.