This is for mainframe use, not consumer. System-Z has never been x86 compatible, but it's not like they run microsoft Office on this.
As for the consumer vs pro question, it's probably a mixture of both. You get the volume from the consumer, so economies of scale, and then the high margins on the pro segment. It's a natural extension. I doubt either nVidia or AMD could survive without covering both segments exactly the way they do.
Most pro cards are just consumer cards with 1/8th less ram for ECC (the latest pro cards, you can choose like 7 GB ECC or 8 GB non-ECC, on the fly), and then they charge 5 times as much for the driver, which you get support if it doesn't work.
Paying a few thousand dollars for a card, or 150k for a server, isn't a big deal for most corporations. The price of software licence and support is way higher than the hardware, usually.