I'd say the true target of this criticism is content-aware platforms, as opposed to content-neutral platforms, which I believe are what people often mean when they talk about "closed" and "open" platforms. The author favorably mentions targeting Windows and Mac OS, which certainly are proprietary, but they do not restrict the user of any content, essentially dumb pipes from hardware to content; these content-neutral platforms would be OK to build a business on. Platforms mentioned as bad were the iPhone, Twitter and Facebook, platforms where the vendor can and does restrict their users' access to content via arbitrary changes to their usage licenses, and such content-aware platforms are shaky grounds to build a business on.