While true, I think many such instances are typos, not lack of knowledge. I have trouble with homonyms. My fingers just seem to type the first one that occurs to them, whether that is the correct one or not. I have to proof read very carefully. And I still miss some, particularly "their" and "there", rarely the triple "to", "too" and "two", but occasionally the first pair, just as an ordinary typo. With repeated letters, it's easy to miss one.
I do the same thing when typing, but not when writing by hand- I have always wondered why.