Why is There More Than One Global Navigation for B2B Company Web sites?

It seems—no matter how many sites I see or create—that the global navigation is almost always the same. Is this a coincidence? Or is information architecture much more of a "global" concern than a project concern? Every global navigation—for B2B companies anyway—is always the same: About Us, Services, Clients, News. Sometimes About Us splits up to include Case Studies or White Papers. Sometimes Services is Solutions or Offerings. Sometimes Clients splits up to include Case Studies. Sometimes News is Press Releases. Beyond these small differences, the information architecture is almost always the same. So, why do we (as an industry) spend so much time worrying about creating navigation for our clients? It seems plenty useful to create a general navigation that covers a wide range of clients—say, B2B clients. But, why spend any time for *each* client on this? Why not just get the navigation that applies to their type of company? A lot of new navigation seems to be new for the sake of being new, maybe for the sake of justifying the information architecture expense. At best, custom navigation is prioritization of which kind of content is best featured for each company. Too often, it includes nomenclature adventures which only confuse the audience. In fact, it might be good to have a stock navigation. After all, people are largely habitual on the Web. A reliable type of navigation probably makes it easier for them to find what they want instead of learning (yet another) kind of new navigation.