Wow, that's fascinating, McAster. I hadn't seen it -- thanks for posting this!
Another link you might want to try is this one:
http://www4.uwm.edu/FLL/linguistics/dialect/index.html
Its from Professor Bert Vaux at Harvard University he has done a study about regional differences in speech and word selection. For example the difference pronunciation of AUNT in different parts of the US and the different terms used for a soft drink or water fountain.
McAster, the problem with the stuff at your link is that the texts are read rather than given impromptu. Listen, for example, to the Jamaican speaker. It contains so very few of the features that Jamaican English is known for because the woman seems to be trying very hard to speak "proper" English.