Nobody likes to receive form letters, just like nobody likes their call to a customer service center to be answered by an agent reciting some form script and answering our questions with equally canned responses (not to mention having our call answered by an automated answering service that doesn't even let us talk to a human being). We all appreciate getting individualized service that reassures us that the person answering our service request has thought about, and is answering, our specific request. Conversely, getting a canned response, whether it's from a journal editor or anyone else, makes us feel dehumanized, unappreciated, and unvalued, as if our request was not even thought to be worth the minimal effort of crafting a simple English sentence for. In this age of increasing automation it also makes us wonder if our request was even looked at by a human at all, and can leave a nagging suspicion (especially among the more neurotic among us) that some error might have occurred and that the response we got is simply incorrect.
With that said, for a journal editor to provide an individualized response to authors is not an ethical obligation; it is simply good service. Like any service provider, some journal editors provide good service, and some don't, either because they care less about doing so or because their workload simply does not afford them the time to do so. If as a "customer" you are unhappy with the service you got when submitting a paper to a journal, the sensible thing to do would be to avoid submitting to that journal in the future, and to avoid supporting that journal by refereeing papers, suggesting to colleagues to submit there, etc. (Indeed, there are several journals that are personally on my black list due to mistreating me in various ways as an author in the past.) Presumably a journal providing poor service of this type to authors will become less successful than a journal that provides good service, all other things being equal (which of course they rarely are).
TL;DR: The practice you describe may not be the best policy to ensure the journal's long-lasting success, but there is nothing unethical about it.