I think it has to do with the fact that we all are cognitive misers. Just think about the comments that this post has generated. Do you really think that every commenter has carefully thought about the subject before articulating an answer? Everyone here is probably forwarding his own pet theory, myself including.
We all probably carry a lot of inaccurate beliefs with us and never bother to check them. Reevaluating our beliefs costs time and effort, keeping the status quo in our mind is effortless. So we only reevaluate when there are strong reasons to do so. As long as people can get away with a belief without being socially reprimanded for it, most will do so. Why bother, since we all probably have more stuff on our todo list than we can manage?
We're all familiar with false popular memes that spread faster than they can be stomped out: You only use 10% of your brain. Al Gore said he invented the internet. Perhaps it doesn't surprise you that some memes in popular culture can't be killed. But does the same thing happen in science?
Most of you have probably heard of Broca's aphasia and Wernicke's aphasia. Every textbook and every college course on language and the brain describes the connection between damage to these areas, and the speech deficits named after them.
Also, both are probably wrong. Both areas were mistakenly associated with their aphasias because they are near or surrounded by other areas which, when damaged, cause the aphasias. Yet our schools continue teaching the traditional, erroneous story; including a lecture in 9.14 at MIT given in 2005. Both the Wikipedia entry on Wernicke's aphasia and the Wikipedia entry on Broca's aphasia are still in error; the Wikipedia entry on Wernicke's area has got it straight.
Is it because this information is considered unimportant? Hardly; it's probably the only functional association you will find in every course and every book on the brain.
Is it because the information is too new to have penetrated the field? No; see the dates on the references below.
In spite of this failure in education, are the experts thoroughly familiar with this information? Possibly not; this 2006 paper on Broca's area by a renowned expert does not mention it. (In its defense, it references many other studies in which damage to Broca's area is associated with language deficits.)
So:
References
Bogen JE, Bogen GM (1976). Wernicke's region—Where is it? Ann. N. Y. Acad. Sci. 280: 834–43.
Dronkers, N. F., Shapiro, J. K., Redfern, B., & Knight, R. T. (1992). The role of Broca’s area in Broca’s aphasia.
Journal of Clinical and Experimental Neuropsychology, 14, 52–53.
Dronkers NF., Redfern B B., Knight R T. (2000). The neural architecture of language disorders. in Bizzi, Emilio; Gazzaniga, Michael S.. The New cognitive neurosciences (2nd ed.). Cambridge, Mass: MIT Press. pp. 949–58.
Dronkers et al. (2004). Lesion analysis of the brain areas involved in language comprehension. Cognition 92: 145-177.
Mohr, J. P. (1976). Broca’s area and Broca’s aphasia. In H. Whitaker, Studies in neurolinguistics, New York: Academic Press.