Ah, you found the rule for when you don't use it. Contrary to many textbooks, teachers, and websites, the lack of an apostrophe in "its" is not an exception--you don't use the apostrophe for pronouns. "His". "Hers". "Yours". As apposed to "Jack's", "Julie's", "the user's".

"opposed".

Normally I wouldn't correct you, but this being the grammar nazi thread and all...

"Its" is only used in places where "his", "her", and "your", which don't have the s's, are used. People don't use "its" in places where they'd use "hers" or "yours". It's awkward.

That's a better example. My explanation was wrong, but it's still an exception in the context you provide.

Bob's house. The mayor's key. The people's choice.

Those are nouns, not pronouns.

Sorry, I used the wrong terminology.