Though you have a point that misspelled words can also lead into a different meaning of the OP, so for the fact that they must expand their knowledge or even their vocabularies just to have a good quality of posts that doesn't need any correction from the readers.
(If they're going to be hard on this then I think that it will not be fair as for the reason typo errors as I know are just written by accident.
Yes, you were right, some people are not noticing those wrong spelling words because they are already used to read such a typos. But not because they can understand wrong spellings words doesn't mean that we will keep posting sentences with wrong spellings. It is much better and more understandable if we correct it.