With some expressions, those who don't, against the grain, force their readers to double check the parsing. The cost may be only a millisecond or two but it is nevertheless a tiny distraction incurred because someone can't be bothered to follow a simple rule taught in primary school. In the glorious future envisaged in the comment, everyone will ignore the apostrophe so all of us will have to do a bit of extra scanning. What's superior about that?
Is it really that difficult to remember that the apostrophe in it's (for instance), is always without exception used as an abbreviation for 'it is' or 'it has', not an indication of possession and thus your's is wrong.
From someone who had issues with this for years, just parroting the rule as you did doesn't help, it only made sense after learning the reason why: the possessive form "its" is grouped with "his" and "hers", not "vixen99's" and "Izkata's".
Speaking of clarity vs confusion, and forcing readers to double check parsing! Muphry strikes again.