"But Western students who sign up for a class in it soon discover that nobody speaks this “standard” as a native tongue; many Arabs hardly speak it at all. "

This is not completely true! I'm a native Arabic speaker and MSA is the official language of newspapers, news segments, and legal documents, governments speeches even wedding invitations and not to forget the Quran and the Arabic bible. So it's spoken and written widely but people tend not to use it that often because it's easier to use shorter words that most of the time sum longer sentences.