> "It's" is a contraction for "it is". No apostrophe is needed.
No. "Its" is a possessive, which puts it in the same class as words like "his" and "hers". If it were a contraction for "it is" then you'd definitely need the apostrophe.
You're parsing the paragraph wrong. The sentence "No apostrophe is needed" doesn't refer to the immediately preceding sentence, it is referring to the original use of "it's" by JarekS.
Ah well. Someone on the internet was wrong, I had to correct them. :)
You're writing your paragraph wrong - the last sentence was incomplete. Something like "No apostrophe is needed when using the possessive its." would have made the object of your sentence much clearer.
One of those other basic but trial-and-error rules of English: don't implicitly refer to something that's a long way away (in this case 4 phrases distant) from your sentence or someone will misunderstand you.
No. "Its" is a possessive, which puts it in the same class as words like "his" and "hers". If it were a contraction for "it is" then you'd definitely need the apostrophe.