Of course there are many other skills involved besides programming, but I don't make the big distinction you apparently do. For example, the part about storing

Of course there are many other skills involved besides programming, but I don't make the big distinction you apparently do. For example, the part about storing data optimally is going to be handled by the database in most web applications, and using that tool well is a distinct skill set from both front- and back-end programming. Indeed the latter two have far more in common than either has with designing an efficient database or optimising queries that access it, or with designing a good UI for that matter. At the very top of each field, sure, there will always be those specialists who live and breathe that subject and can do the things no-one else can, but most people will never achieve such proficiency in any field during their career and most businesses will never hire anyone on that level, so I'm not sure it is going to generate much insight to talk about extreme cases. For anything below elite levels, you certainly can have the same person with expert skills in both front- and back-end dev, or in back-end dev and DB admin, or in front-end dev and UI design, or just about any other combination of relevant skills.