You're absolutely right; Most advances do eventually trickle down. But, most advances in FOSS have benefited users who are less well off, making computing, both libre and in general, more available to them. It's frustrating that in order to get a truly free computer one has to pay about the equivalent of 3 months wage, which is a no go for most people I know.

While I agree with you, the average buyer of computer components is used to spending an order of magnitude less on a motherboard. A person can go to their usual source of computer parts and pick up a motherboard for a couple hundred USD at the high end. A few thousand USD for motherboard that does not offer an order of magnitude improvement in raw speed or expandability is going to be a very hard sell.

The question is rather: Is there a large overlap between the people who can afford to spend thousands of dollars for a free (as freedom) POWER8 workstation and the open source idealists who would love to buy such a free device?