How does it make a difference from a legal perspective? I am a former lawyer and can't see how any of this matters. I have thought about this deeply in the past (dealing with the same issue for another app), and talked with IP lawyer friends, and we cannot determine what basis Apple has for singling out apps that are essentially specialized web browsers.

I'm happy to be enlightened on why this practice makes sense, but so far I've come up with nothing.

The Fair Use Doctrine allows someone to share copyrighted material for a limited and "transformative" purpose. Typically "transformative" falls into one of two buckets: parody or commentary/criticism. Reddit, Twitter, Facebook and Instagram all display the entire news article within their app only after it has been presented alongside the poster's commentary. OP's Hacker News Zero app does it the other way around. Click on the link and you're taken directly to the news article and, if you then choose, you can select the "comments" to view commentary/criticism. The initial viewing of the article doesn't fall within Fair Use because it's not transformative in any way.

I suspect if the app is changed to operate more like Reddit (view the article title/source and view comments, if any, prior to opening the article) it would be approved by Apple. Alternatively, as suggested by Apple, the app could initially present only an excerpt of the article and fall within the exception but, as pointed out in the medium post, that probably isn't particularly valuable to HN users.

You also could have tried reading the link I included with my original comment.

This begs the question of why the fair use doctrine is required at all. It isn't needed for a web browser; why would it be needed for a pared-down web browser? Is it needed for a text-only web browser?

None of these is addressed by your original comment or the link, which all presuppose that the fair use doctrine is the only way to escape copyright problems associated with loading a webview with someone else's content.

Web browsers have an "implied license": https://en.wikisource.org/wiki/Field_v._Google,_Inc. and (I believe, but don't quote me on this) the law was amended shortly after this case to clarify the permissions/limit liability of web browsers & ISPs.

A third-party application doesn't have the same permissions/protections. Copyright law doesn't always require the author's permission though. If you don't have permission you can still display the content if you have a legal justification. The Fair Use Doctrine is the set of factors to determine whether or not publication without permission is justified.

The transformative nature of the publication is only one factor, although it's the most important. Another factor working in OP's favor is that the use is non-commercial. He says in his blog post that he maintains the site on his own in his spare time, doesn't charge users to download the app, and from what I can tell, doesn't have any ads.

I really think OP could make some small changes and get it approved by the app store.

Really unclear to me what you man by "third-party application" here. How is Google Chrome not third party, but this app is?

Typically in this nomenclature the first and second parties are the user and OS (or computer) vendor. The third party is an application developer. So typically Google and Mozilla would be third parties the same as maker of the HN browser.

Aside from that, I see no real distinction here. When I launch Firefox, it shows me on my "blank" home page (provided by the browser, not a web page) a list of popular articles curated by its Pocket division. This is essentially identical to what OP's app does. One is a browser that proffers links, the other is a browser that proffers links.

In Google Chrome, you have to type in the address of website you are visiting. It is a lot of different if Chrome showed content from other sites without you specifically requesting it and without showing URL of those articles.

I have seen of lot of funny or meme apps which rip content off same popular websites. I think it unfair to operator of such sites. A lot of these app will show their ads, but won't pull in ads of publisher.

But they are specifically requesting it.

I think this is a bad argument. Showing web content is how the web works.

The Field vs Google case is about the Google cache, not web browsers...

Publishing a hyperlink has nothing to do with Fair Use. OP is not re-hosting the content themselves, therefore in no way does Fair Use Doctrine apply.

The key difference is, Twitter and Reddit are big. The app store rules are way more flexible, when you have millions of users.

That's not the key difference here. The key difference here is that the content author has control of the output. In the app in question, the app is scraping the content and the app developer is choosing how it's outputted. That's why the app is in violation.

Reddit is not the content author.

I never said reddit was. The app in question isn't exclusively limited to content on reddit. Since anyone can post content from any website on Hacker News, there are several content sources and none of them are being displayed natively in this app.