Web skills such as graphic design are not the only ones that are often provided on a temporary basis. Several other professions are routinely hired on an as-needed basis. Technical writers often work on a project basis, and they can be found through specialized agencies. Software testing, too, is often staffed with temps who move from test phase to test phase like migrant farm workers moving from one harvest to the next. A rule of thumb is that you can find talent more readily than management.
Management provides the continuity and long-term view while worker bees can come and go.
I know a company that went as far as to lay off all their full-time technical writers, retaining only the documentation management. They maintained that while it was easy to hire writers when they needed them, good managers were difficult to find. I wasn't surprised to learn that it was the documentation group managers themselves that came to that conclusion. The good news is that those writers, or at least the ones I know of, have little problem finding a variety of interesting work. There seems to be no shortage of opportunities for contract workers in the IT business, and no shortage of agencies to fill them.