This is such an interesting topic!
I'd like to present three sources about difference in accents and the perception of "class" in relation to accents.
This first is a passage from "The Linguist," a site at Eastern Michigan University. This is from an article by Anthea Fraser Gupta (With input from other panelists), School of English, University of Leeds.:
"¢ Is there a Standard English accent?
There is not a single correct accent of English. There is no neutral accent of English. All speakers of English need to cope with many different aspects and learn how to understand them. Some accents are associated with social groups who have high prestige (the kinds of accents spoken by highly educated people, for example), but there are also many of these high prestige accents, all of them regionally based. The accents that are traditionally taught to non-native speakers of English are high prestige accents from various places.
The two most commonly taught accents (in the world as a whole) are both rather artificial: 'General American' (more or less a Mid-Western and West Coast accent, and used by some high prestige speakers outside this region too); and the British accent 'RP' (which developed in the private boarding schools of the nineteenth century, and is associated with high prestige groups in England). Both these accents are used over a wide geographical area, though in world terms both are regional accents (General American is a US accent, and RP is an accent of England). They are heard more, by more people in the country, than are accents which are associated with a smaller area: so people are familiar with them. These accents are the ones transcribed in dictionaries. Because they are used over wide areas, and used by people of high social class, they are seen as being suitable to teach to foreign learners of English. For this reason, they are called 'reference varieties'.
When radio was developed in the early twentieth century, many radio stations in the US and the UK selected their continuity presenters and news readers by their accent. So 'General American' is sometimes known as 'Network English' and 'RP' is sometimes known as 'BBC English.' The effect of these policies of course was to add even further to the prestige of the reference accents, and to increase the population's exposure to them. The BBC, incidentally, no longer has this policy and now uses news readers and presenters with a wider range of accents.
In all languages some accents have higher prestige than others. Tests of judgment have been made in many languages which show that people within a community often share judgments. In the UK, for example, the accent associated with the city of Birmingham consistently comes out as being 'ugliest' while London accents tend to be heard as 'criminal'. These judgments are based on stereotypical associations. f British accents are played to Americans, they do not make the same judgments, because they have not learnt to associate different British accents with the same stereotypes British people have. In the US many speakers are prejudiced against 'Southern' accents, but British people would not judge Southern accents badly in the same way. Judgments like this are not based on anything in the accent itself -- if different accents of English are played to Russians who speak no English, they cannot distinguish the high prestige from the low prestige accents.
You should try to speak neutrally about different accents, and not suggest that one accent is better than another.
The reference varieties are not 'Standard Accents', because no one is required to use them: compare this to spelling -- we are expected to use the Standard Spelling and do our best to correct mistakes. The reference varieties are not more 'careful' or more 'correct' than other accents -- it's just an accident of history that their speakers were the ones with power.
_______ The second is an article – a long article – in Wikipedia about Received Pronunciation (known as RP), which had been held as the standard and the best pronunciation in British English for some time. It tells a lot about how an certain accent can become prestigious.
The third is a definition from the American Heritage Dictionary* of "General American," and an article from Wikipedia about General American. In the definition and in the article, you can see the General American is kind of Midwestern English, without the regional accents that Richard has noted. URL=http://www.answers.com/topic/standard-midwestern]http://www.answers.com/topic/standard-midwestern[/URL]
This variety of English has been the standard for newscasters, but it is regional or learned.
It is not based on class.
*The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company 2007