Specialization allowed for mass production. Specialization also drives costs out of the system. Let's just say a company chooses to move its own raw materials - it needs transportation, drivers, docks, handlers, claims and customs agents, etc. All of these costs and inherent direct and indirect labor costs are absorbed by a manufacturer who is in the business of making pipes, not transportation. Now it becomes the middle-man's job to drive cost out of the system.
Specialization is the engine that is driving most companies away from vertical integration.
Logistics and Distribution is the key to the miracle of our capitalist system. Edison didn't invent the lightbulb or electricity, he devised a way to distribute it throughout a house and a city. Ford didn't invent the automobile, he created a system to better produce it. The United States can feed the world because of an incredibly integrated logistics system of roads, waterways, railroads, and air transportation - while equally rich in resources countries' people starve while crops rot in the fields. Products and services are no good if they cannot get to the final consumer.