As Odlin (1989: 58) points out,

Differences related to expectations about coherence in discourse may create special problems for learners in their reading or listening comprehension efforts. Alternatively, those differences may lead members of a speech community to consider the speech or writing of non-native speakers incoherent. It is not yet clear just how often such differences actually result in negative transfer. What is clear is the potential that cross-linguistic variations in discourse have for creating misunderstandings.§

More specifically: How do differences in standards of logicality and relevance among speech communities within the same language affect their production and understanding of written communication?

Or, perhaps more to the point, when will educators abandon their misguided emphasis on prescriptive grammar in favor of the structural properties of written texts?

§ Odlin, Terence. 1989. Language Transfer: Cross-Linguistic Influence in Language Learning. Cambridge: Cambridge University Press.