The U.K.'s relationship with Received Pronunciation is very different: it is the native regional accent of the rich elite of London, and consequently it would be quite unusual for a homeless man on the streets of Liverpool to speak it.
At the very least, General American is an accent that can be spoken without revealing anything of one's birthplace and social situation. A man speaking R.P. reveals his wealth and upbringing around London to a greater degree.
The Finnish situation, for comparison, is that the standard language is spoken by about no one informally, and is a practically constructed languages that was created by the government by combining the most conservative elements of all dialects. — it is the native language of no one, so it is even more neutral territory than G.A., yielding kno one an unfair advantage.
Getting rid of latin as the lingua franca was a huge mistake.
The author seems to be writing for a U.S. audience, so most of his examples come from North American English. Similar problems also exist, of course, in other English-speaking places and in other languages. People in Britain, for example, are famously sensitive to class and regional differences in speech. In Japanese (I live in Japan), regional accents and dialects can vary greatly and are also sometimes associated with prejudice and discrimination.
For some languages, a national government might try to fix the pronunciation, grammar, and orthography of a “standard” language. In the 19th century in Japan, there was a partially successful government-led attempt to make a version of Tokyo Japanese standard; school textbooks and, later, the national broadcaster NHK mostly adopted that dialect. The government has also influenced how Japanese is written; the forms of many kanji that now appear in Unicode, for example, were originally decided by government fiat after World War II.
One interesting aspect of American English is that notions of what constitutes “standard” American English—including even spelling—have formed largely independent of the government. Publishers, broadcasters, educators, and a variety of complex social forces have had much greater influence.