Supporting a second platform is indeed a significant investment. I'm aware of that - I'll never develop for iOS because that would mean I'd have to buy a Mac, buy an iOS device, learn Objective-C/iOS development, and how to navigate Apple's app approval gauntlet. However, there's a big difference in the numbers when you have an app with a lot of users. For example, you can have someone else make the app (which, to his credit, Marco did do after years of foot-dragging).
Your point about competing functionality is moot, because that means he should abandon iOS as well. In fact, in that case, he should favor Android, since's Apple's draconian app approval policies means that Instapaper could suddenly get kicked out of the app store without notice.
In any case, allowing Marco's blog on HN means that it pushes more other, more valuable content out of the way. By banning sites like his, we wouldn't have to waste time wading through his mindless drivel to find useful links.
Your point about competing functionality is moot, because that means he should abandon iOS as well. In fact, in that case, he should favor Android, since's Apple's draconian app approval policies means that Instapaper could suddenly get kicked out of the app store without notice.
In any case, allowing Marco's blog on HN means that it pushes more other, more valuable content out of the way. By banning sites like his, we wouldn't have to waste time wading through his mindless drivel to find useful links.