That's a pretty good summary. I always figured the nasally, fast, brief New England speech pattern was related to the cold. As well as the attitude and general outlook on life.
Nah... Northern Rockies is north and we have a drawl... different from all y'all, but the same. I can normally talk eye to eye with a Texan, and barring normal regional colloquialisms, we understand each other just fine. the change is somewhere south of Colorado, and west of Oklahoma though desert rats down in Arizona, Nevada, and New Mexico sound like they talk like me... other than the Mexican flavoring...
But we understand your'in, y'all, fixin to, and etc, as it is part of normal conversation.