My point was not clearly made. I'm not talking about vertical or horizontal, I would put them both in the "technical" category of scaling. I meant to say that

My point was not clearly made. I'm not talking about vertical or horizontal, I would put them both in the "technical" category of scaling. I meant to say that scalability is not something that can simply grow to meet a certain load, it is a concept that your system "can survive at scale" in whatever form that scale takes. It encompasses many things like having more servers, bigger servers, more people working on the servers, more users, longer sessions, more activity per user, supports more features, and so on. It's a semantic point, but it seemed like the author had a very narrow idea of the terms he was using, and was complaining more about his own definitions than the concepts themselves. And the user cares about all of them, indirectly. They all matter because failing at any one of them are reasons to use something else, whether it's simply slow performance or because your high performance system is so brittle you can't evolve, or downtimes because your high performance, quickly evolving system requires more admins than you can afford, and so on.