Anytime you write over a certain number of words - probably 200, maybe less - anyone will make a typo. Brevity has many advantages, and that's one. It doesn't matter how well-versed in rules or skilled in typing or writing as a craft, you'll hit the wrong key, change one thing on the fly and not make a needed secondary change.

Hell, I shift my fingers the wrong way and it's just gibberish. Sometimes I type by watching the keys.

Of course, internal sources (eds, internal advance readers) should spot the errors.