Do you have any idea what goes into editing a printed publication? In a good publishing environment, no one editor is ever the sole person to check mistakes on any given document. When I worked at a small newspaper, people were still finding errors when the paper was being posted to boards just before being sent to the printers, including stupid little ones made by people who should know better. It's not because the people involved were morons--it's because they're humans.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.