The article specifically mentions services dropping support for the RSS format in favor of proprietary apis. This is bad. RSS/Atom might be falling out of favor due to XML's own decline of popularity but it needs to be replaced by something else, not per-service programming.
I think it's a mistake to attribute RSS's decline to any sort of technical issue like "XML's decline". There's nothing technical about it, it is strictly social. RSS is a way to move content out of the walled garden, and they want you in their walled garden. That's it. That's the whole story. They are rejecting the very philosophical underpinnings of openness that were the reason for the creation of RSS in the first place.
You are right that the decline is social, but it's not because "they" want anything. RSS was never a technology that managed to catch on outside the uber-geek crowd. I use "uber-geek" intentionally because it seems to me that most tech-savvy people I know don't use feed readers (in their browsers or otherwise).
I think you're conflating 2 things: RSS as format read by people and RSS as a format read by machine. Don't let the lack of popularity of the former sway your opinion of the latter.
Having to write custom code for each service you're interested in sucks compared to adding some RSS endpoints into an array.
