Some editors I've worked with have been very draconian about it, to be honest it shouldn't happen if three sets of eyes are proof reading a story... Still happens tho', obvs... I always enjoyed spotting them when I art checked a layout before sending it to press, so, so satisfying...
Spotting editorial mistakes at pre-press check stage is ~one of my biggest pleasures in life~ a solemn duty and one no designer should take pleasure from
EDIT: strikethrough text fail. where's an editor when you need one?!
If the Grauniad fired every sub-editor who made a mistake they wouldn't have any left ;)