Games Workshop has had editors since day 1*. The fact they now have an opening for an editor/proofreader means only that someone left or they are expanding the crew. Having an editor/proofreader doesn't guarantee that a product will be free of errors, especially with a body of work as broad and diverse as that which Games Workshop publishes.
Yes, it's frustrating when seemingly obvious errors and inconsistencies are found in professionally published works. We don't need to use this job opening as an opportunity to take cheap shots from the peanut gallery, though.
To those of you that meet the qualifications and either currently live at/near or are willing to move to/near Nottingham, UK, good luck.
* The editors on the 1st edition Warhammer 40,000 Rulebook ("Rogue Trader
") were Jim Bambra and Paul Cockburn. The proofers were Mike Brunton and Lyndsey De Le Doux Paton. I'm sure we could examine GW
products published prior to that book to similarly find editors and proofers.