I used to be one of those people who thought I knew The Right Way and that everyone doing it Wrong needed correcting. Here's an always necessary reminder that there is no such official, inarguable correctness in English.

One good example is in that article itself. The common teaching is that 'which' is for nonrestrictive clauses and 'that' is for restrictive clauses -- but as you can see, it's perfectly normal, natural, and comprehensible for speakers of certain dialects (let's say Commonwealth) of English to use 'which' for restrictive clauses.