But what about the other examples I've named?
A university sells education. Classrooms, dorms, teachers, etc. are all part of the same 'supply chain' for education.
A trial lawyers sells legal services. Research, evidence, appearing in court, and so forth are just incident to the basic legal service provided.
A restaurant sells a 'dining experience'. The food, wait service, and so forth are all part of that same experience.
What OP means by a company that has both horizontal and vertical businesses is a company offering something as a standalone revenue-generating output (the "horizontal" business) and something else that incorporates that standalone output as part of another output (the "vertical" business).
This would apply, for instance, to a fast food company that not only sold hamburgers via its chain of fast food restaurants (vertical) but also supplied those same hamburgers to other, possibly competing competing fast food restaurants as a separate business (horizontal).
* Tesla - sells devices (cars) and services (auto repair, charging stations, consulting, etc) * Equal Exchange - sells devices (Cocoa, Coffee and Coffee gear, etc) and services (reports on working conditions and other quality control data) * A private university - sells devices (classrooms, living space, all sorts of retail items) and services (classes, research, community outreach, much more)
(getting more abstract)
* A trial lawyer - provides devices (a body to stand in place of a defendant, relevant evidentiary media materials) and services (research, strategy, etc) * A restaurant - provides devices (table, food, decor, ambiance) and services (cooking, consulting, food sourcing)
OP may say that the intended target of this critique is the "tech" sector (ie, "a horizontal business should be great on every platform, while a vertical business should be differentiated"), but it looks like that becomes a capricious distinction the closer you look.
A university needs to provide compelling courses on research from all sources, including other institutions of higher education, while still being differentiated in its "vertical" market.
A restaurant needs to source food that will excite its clientele (again, even sometimes from various types of horizontal competitors) while still being vertically differentiated.
And so on.
Providing both horizontal and vertical components (whether organized into separate subsidiaries, subcontractors, divisions, or whether blended entirely) is a very old concept and is the natural course of maturity for a successful model.