I read the Guardian almost every day, and I clapped heavily for your article, but the Guardian's proofreading has been notoriously uneven over time, which is why they have the affectionate nickname of "The Grauniad" (get it?)

They're much better these days, and they have a sense of humor about it, but I still find tiny mistakes a couple of times a week (but then, I'm that sort of nitpicker).