That's sort of confusing. In a number of places I've read an explanation that what is described in the Wikipedia article as "Mid-Atlantic English" was in fact higher class New York English before WWII (one of its most characteristic features was a non-rhotic "r"). These sources also tend to use Franklin Delano Roosevelt as an example of this sort of accent.
For example: http://en.wikipedia.org/wiki/New_York_dialect#History (that article quotes the