I'm a big stickler for spelling in things too, especially if its something that is meant to be a finished product. I don't notice it too much in game, mainly because I don't read things, that's right, I don't read any mission boxes except to know what the mission entails (timed, kill, door). And yes, I know this could be misconstrued by many to mean I'm missing content, but to each his own, I've been here since Beta and I just love being a superhero without all the silly story.
It does, however, drive me crazy when I see it in online articles at cnn or something. I send a lot of emails like that.
Kudos to you though for all the spelling corrections, you're helping make the game better.