All proprietary OSes are supported by their respective publishers. For example, Microsoft supports Windows, IBM supports AIX, and HP supports HPUX. This provides a single contact point when IT staff needs service.
Linux, being a free OS, is not supported by any specific organization. Some commercial entities, such as Red Hat, offers support for the cost of annual service contracts. However, due to the open source nature, Linux can be supported by any group of experienced developers and/or administrators.
Because the DMCA does not apply to Linux, users (administrators, developers and end users) of Linux can freely share their knowledge with each other. In fact, one can often find support via online forums and even live chats.