The whole problem is that they are indeed conceptually similar, but definitely not equivalent and definitely not interchangeable.
If this were an automotive forum, it'd be like the difference between diesel and unleaded. Yes, they're both liquid fuels, commonly used in automobiles. But at a technical level they're very different things, and you cannot put unleaded in a diesel engine and expect to have a good ending. And we see people doing that, often enough, that we want to be clear on what is actually going on.