The US ones are largely siloed collections of companies across a spectrum of industries.
The Japanese ones are strongly vertically integrated. I was told when I was sponsored by Yamaha for international ski racing competition and at one of their testing camps: 'we mine the ore, make the metal, make the machines that make the tools, make the tools, and then use the tools to make the products'. It's about both controlling the quality all the way up and down the value chain, and also capturing the value-add all the way up the chain (not sure how much of each).
I was quite impressed by their quality and technology, which was the prime reason I went with them. At the time, they were one of only two companies worldwide that could make a pair of skiis that was actually indistinguishable left/right to racers at our level (the other was Fischer which dominated the Swiss, Austrian teams and we wouldn't get their best race stock), and Yamaha had amazing ability to tune the performance properties. I'm quite sure that they could do it because of their strong vertical engineering and QA integration.
(Always seemed like a superior model to me, but I'm not a big biz guy, so what do I know?)
Edit: typos,clarity