As the SCO history has demonstrated, the Linux kernel is not based on a commercial operating system. It is a implementation of a POSIX style operating system with a clean source history. POSIX itself is an open standard. The user space is a mix of many packages some based on POSIX standards (e.g. shell, file utils) others based on common application needs. Many of those are indeed based upon open industry standards.
Wikipedia material is not as well vetted IMHO and given the volume of material, there is a greater possibility of something being copied incorrectly. But much of the material we are discussing is basic scientific fact and could reasonably be based heavily on material available via sources like Project Gutenberg. Other material would be newer and likely could reference open sources.
As for organization, the courses follow standard outlines so university programs can receive accreditation. And building up material from basic to advanced concepts in a framework that could only allow 8-16 chapters per semester doesn't allow that much variation.