Interesting. The reason I find it worth pointing out is that the "entity" and "component" parts are not really that interesting by themselves. You could have an object-oriented "entity-component" system where components encapsulate game logic, for instance. It's the separation of game logic into the separate "systems" that is interesting. That said, the actual implementation of "systems" varies so much that it's not surprising people focus on the "entity" and "component" parts.