But publishing it takes effort, and if usage isn't high enough people might stop.
And, frankly, that's already a dubious claim and getting more dubious. An RSS subscriber is very "stickied", and thus very valuable in a lot of ways. I mean that even beyond mere money. A lot of the other putatively "better" approaches are a great deal less powerful, again, because you don't own it, the "better" service does. Witness the way Facebook decides whether or not your "subscribers" get to see your posts, making them a great deal less valuable than an RSS-subscribed reader. I expect this to play out over and over, and for RSS to retain its position of indicating "I am a serious subscriber" for a good long time.
Facebook et al can offer you a better short-term outcome, but as such things scale up, the incentives pretty inevitably turn towards trying to capture the value of your subscriber base themselves. RSS disintermediates that fairly successfully. And since nothing particularly stops you from offering that on the side... why not?
It's much easier to go to /rss and get the content than have to coordinate with however many teams and organizations it took to create all those sites.
Probably not coincidentally, that's about when I started using HN.
I absolutely love it. Unfortunately, I had to give up on using it last week since I had too many feeds to stay on the free version.
I'm now using Digg's Reader and I'm happy so far. Updates more often than (the free version of) The Old Reader too!
RSS was there before Facebook and Twitter.
RSS will be there after Facebook and Twitter.
One of the neat things about RSS is that I don't have to care whether it's the Most Popular Thing. I just need a reader, and someone publishing it. No "boil the ocean" required. I used RSS back when the number of publishers could be counted in the dozens. It was still a useful technology!
If you're then inclined to argue "but what if everyone stops publishing it?", a "boil the ocean" of its own, my response is that I'll worry about that when it happens. That would take a lot of people to stop publishing it, and... in modern times, it's so easy to publish RSS, and you own it, not like your Twitter or Facebook integration, so I don't expect the value proposition to go sour for everyone for a long time. (And I don't really have to worry about all the readers going belly up, there's enough open-source desktop readers if nothing else. To say nothing of the open source server-delpoyable ones.)