I can't imagine a class of office workers that I wouldn't want to have Internet access. Having access to Wikipedia straightforwardly increases your knowledge about everything.
Wikipedia is not a sufficient justification for internet access because it is fairly easy to put a copy on the company LAN or even on each desktop.
Distraction is a Symptom of a Deeper Problem: The Convenience Principle and the Destruction of American Productivity is a good article on distractions versus getting things done. With extra emphasis on how many of our distractions are the result of a desire for convenience rather than something more substantial.