Regarding the use of the apostrophe, I don't have any proof but I think it's more often native speakers rather than non-native speakers that make theses mistakes. Especially it's vs its. I would be really curious to have stats on this and more generally on the categories of errors that non-native speakers make compared to native speakers.
I think it's because a non-native speaker has to learn the grammar in a systematic way, as opposed to a more organic/phonetic way. For example we (non-native) learn "it is" before learning "it's", which I imagine is the opposite of a native speaker.