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Look at it from this point of view.
1. Linux represents software commoditization at the low layer of the platform, i.e. the low layer of the software stack.
2. At a higher layer in the software stack is the vendor product line. The vendor product line is just like a manufacturing plants assembly line. These vendors control the process for assembling a solution, based on Linux. In terms of software production, this is where the money is. If you want to make money producing software, you must integrate your product into this assembly line, so you have to talk to the vendor and ask them how to interface. Companies like Oracle and IBM market their software product at this level.
3. So the background, the low level of the software stack, is open and accessible, it's a testing ground, a ground for experimentation, until you have a concept for a product that you can push up the software stack.
4. Technically Linux vendors have developed a few Linux home desktop products (ex Linspire) however there has not been a real push by the arbiter towards this concept, not yet anyway.