I agree...there is scale and then there is scale. And then there is scale like Facebook.

We need not assume internet FB level scale for typical biz apps where one instance may support a few hundred users max. Or even few thousand. Over engineering under such assumptions is likely cost ineffective and may even increase surface area of risk. $0.02

It goes much further than that.. a single moderately sized VPS web server can handle millions of hard-to-cache requests per day, all hitting the db.

Most will want to use a managed db, but for a real basic setup you can just run postgres or mysql on the same box. And running your own db on a separate VPS is not hard either.