Oldspice- We have always been funny about accent and tend to make value judgements about them; Peter Trudgill has done a lot of work on this. There is certainly a broad correlation between accent and social class. However, particularly in my experience it has little to do with content and many speakers choose to keep their local accent rather than modifying it, e.g Dennis Skinner and the sadly departed Fred Dibnah.
I'm not sure why Standard English is prefered and I suspect it is considered less and less important except for in the highest circles. Many dialects are perfectly good forms of English, but when we write I believe Standard English is best.
Some Nottingham dialect e.g. Didja gerrowt? or woze we isen? mean little to the outsider and it's important to not let spoken local English intrude on the written word. IMO
