A couple of days ago Dave Shea and I were talking about accents, and whether, over time, English speech is becoming more uniform around the world. We didn't come to any conclusions, since we were just chatting and didn't have any research materials on hand.
Will a uniform worldwide English-speaking accent arise in a few decades or centuries, or will Scottish and Texan and Newfoundland and New Zealand accents persist? Is it enough just to understand one another? What about the influence of those who have something else as a first language, but who use English regularly? If an "average" accent does come about, will it be what we might expect today (i.e. some variation on the American/Canadian generic newscaster voice), or something that would seem foreign if we heard it now? Hard to know.
Here, however, are people with 297 different accents speaking the same English-language paragraph. Some of them have English as their first language, some do not.
I think that, while worldwide mass media, jet travel, and telecommunications do have a flattening effect on the diversity of dialects (as opposed to accents), and may tend to dilute accents that are so strong as to be unintelligible to the general English-speaking population, the kind of pronunciation we think of as "an accent" doesn't necessarily come from there. It's obvious that kids don't learn accents from their parents (or teachers, for that matter), but from their peers, and the speech of their peers is a far more immediate and interactive than anything available on TV, radio, or the Web. (Apparently that's even true in sign language.)
TV, planes, phones, and the Net are big factors in the disappearance of distinct languages, which is a whole other issue.