I don't remember it ever being common to have to buy hardware from a specific vendor in order to read the news, a magazine or a book.

It's common for sources of entertainment and/or information to be platform-specific.

I don't think this is true (game consoles notwithstanding). Throughout history, there have been but a few mediums in use at a single time. Most of the time, all these platforms were supported. (Now, it's any number of content distributers on the web, DVD/CD and Blu Ray. 10 years ago, it was DVD and VHS.) The notion of products bound to a specific platform or medium rose primarily with the popularization of consumer computing, and software likely remains the most platform-specific content available.

So you owned a PC and not a Mac in the late 80s/90s then?