Is TV a threat to dialectical diversity?

"Many Americans believe that television and radio are homogenizing our language, making all of us talk more alike. To linguists that is a myth. Despite decades in which we have listened to or watched the same programs, the regional differences in American speech remain vigorous. Paradoxically, the truth seems to be that, where change occurs, it is often creating more diversity, not less" (31).

From Do You Speak American?: A companion to the PBS television series, by Robert MacNeil and William Crain (New York: Doubleday, 2005).