Things used to be much better. Nearly all early computers included complete schematics. My first education about computer hardware came from studying the schematics of the Apple II.
Big, useful manuals scare neophytes. As such, the awesome schematics included on a lot of early systems were removed along with nearly the entirety of the manual because they just added bulk for the majority of users. Also, as boards have gotten more and more integrated, the value of those schematics for someone just getting into hardware has diminished. The boards are now 8+ layers, which means most of the traces are now hidden from view, and the components themselves tend to be little more than a fairly simple power regulator, big huge monolithic chips with hundreds of pins, a few filter capacitors, and a few pull up/down resistors. There's too much "there" there to really be useful for the beginner.
However, this is where the arduino is very useful. It's a small chip, and a small number of components, which would increase the value of having a schematic that people can trace, and keep in headspace what the various lines are doing. More than a bit of me thinks that the ARM chips that are starting to squish the 8/16 bit micro market from above may be useful here. A decent number of pins, decent speed, and something you can hack that does more than blink pretty lights. Perfect for giving a schematic that kids can follow and get to really understand what's going on.
Apple may have felt that they were sufficiently protected by the copyright on their software, including the ROMs. Indeed, Apple defeated a clone maker, Franklin, based on this protection.
Release of the design had an interesting side effect. Since the entire ROM could be disassembled, developers started exploiting un-documented features, for instance by manipulating RAM locations and branching into the middle of routines. A book, What's Where in the Apple II contained hundreds of useful addresses and entry points. As a result, Apple lost control of their API, and could not upgrade the system without breaking popular software titles.
The Apple //e was a heroic effort to preserve software compatibility, but included a bare minimum of new features. I suspect this may have been a factor towards Apple developing their next big thing -- the Mac -- as a closed system.
A similar thing happened to the IBM PC, because developers started hard-coding the known address space of the display RAM, rather than going through system calls, resulting in the famous 640k barrier.
