His reasoning? Most commonly misspelled words are of such ancient provenance that there's no reason for modern audiences to follow blind tradition:
We spell the word "February" the way we do only because it is taken from the Latin word februa, the Roman festival of purification. Similarly, the "correct" spelling of the word "Wednesday" comes from the Old English Wodnes daeg, or Woden's day. But why should we still pay homage today to a pagan god or a Roman festival of purification?
Counterpoint: The same magazine published responses to its annual call for egregious errors made in exams. As reported in The Guardian (oh, the irony!), British students wrote that "control of infectious diseases is very important in case an academic breaks out" and that "flirtation makes water safe to drink."
Copyeditor General's ruling: Sure, I can forgive the occasional typo; I can look the other way when I see uncommon words misspelled. Nobody's perfect, after all.
But when someone who is charged with teaching the next crop of professionals tries to argue that it's okay to half-ass the days of the week or the months of the year--because really, it's not as though you see them in writing very often, is it?--well, then we have a problem.
And if the exam examples are any indication, there's a lot of work to be done.