@joz has given a very accurate explanation to answer this - but one final thought:
Locals are more likely to visit more often, but they're also less likely to spend in park on every visit.
If they feel like they got a cheaper deal to enter, they won't hesitate as much about spending in-park. They've already saved money, so a little in-park spend is ok... every. single. visit. If they just refill their unlimited refill sipper on every visit (about $9) they're making $8 additional profit. Kids want to try that new donut milkshake? cha-ching. There's a new hat-graffiti-cape-embroidery-latest-gimmick store open on main street? try it out.
no, the postcode restrictions are necessary, for the reasons already mentioned above by Joz - tourists will pay more, locals will be more likely to visit if they have cheaper passes.
Most locals won't go near the parks in peak periods anyway, so blackout dates won't change much. (Back when all passes were $99, blackout dates would have worked for a tiered system, and they tried it, and then quickly backed down on it - rewarding the cheaper pass-buyers by allowing them to enter christmas week, while stiffing those who paid the extra for VIP Gold, making the extra money paid essentially worthless.)
People have different opinions
Tone doesn't come across well in written text
Absent the tone that might imply humor or sarcasm, many people misinterpret intention and react to that misinterpretation.
Also - some people are stupid, and because you can't smack some sense into them, they keep coming back with ridiculous unrealistic proposals, and won't accept being told it won't work by logic, reason, or experts in the field. (But that doesn't relate to this current thread).