I think OP was just being an ass, but whether the behavior is opposite really depends on your frame of reference. The lack of apostrophe is consistent with how you deal with possessive pronouns: his, her/hers, our/ours, etc. No possessive pronouns have apostrophes, with one exception. And the apostrophe is consistent with how other contractions work.

If you remember (and care) that its and it's are two separate words, then you should be able think your way through it. It's could legitimately be possessive or a contraction, but its can only be the possessive.

Anyway, I agree with you that it's tricky enough that we shouldn't be assholes about it.