While it was true for _some_ companies in the last 20 years, it won't necessarily remain the same in the next 20 years. Computer business in 1980 was very different from 2000, and it is very different now. And it's not a given that _most_ of the money is being made from third parties.

Even now, most of the top tech companies are known as hardware companies (Apple, Samsung, Foxconn, Huawei, Dell...). Alphabet, Microsoft and Facebook are exceptions. And out of these three, only Alphabet and Facebook thrive on middleman strategy.