Grammar and spelling cannot be easily separated, and native speakers usually study grammar for spelling and punctuation. "видит" is spelled with "и" because it is 2nd conjugation, "видел" is spelled with "е" becuase the past tense is formed from the infinitive and does not depend on the conjugation. Is it grammar or spelling? Then, native speakers do not need to study grammar as foreigners do, they study it in different way. Grammar is a part of school program in Russia. There are theoretical exams (you can choose it) on Russian language. So it is considered bad for an educated person not to understand Russian grammar. And trust me, one cannot put punctuation marks correctly without solid knowledge of syntax. For example, parts of a complex sentence are separated by commas, each part has its stem (the subject and the predicate), but, as you know, a subject and a verb might not be in a Russian sentence (сегодня холодно), so it's not trivial to find a stem, but one badly needs to do that to put commas correctly.