Yeah, but if they did?
Also, do you really think nothing of their Nvidia deal? Nvidia has plenty to gain by giving them lower prices. Also they are making their own case so arguably they are a hardware manufacturer now.
Then it would be going against their current philosophy of an upgradable PC, it would just be a console locked down and stuck in time for nearly a decade. "Steam Machine" is a PC, same as any put out by Dell, HP, Alienware, yourself. Just they've called it "Steam Machine" cos it's better marketing.
Nvidia don't actually sell anything to the end consumer though, so Nvidia lowering prices on thier chips isn't going to do much except give EVGA, MSI, Gainward etc bigger profit margins. Nvidias involvement is exactly the same as it has been with game developers; optimising the software. In this case drivers for Linux since they're usually pretty abysmal. It even says in Nvidia's announcement that that's what they're doing.
Designing thier own case puts them in the same class as SCE, Nintendo and Microsoft? Antec make their own cases, are they now a hardware manufacturer too? Pretty low bar of entry if you ask me. The specs on a case are shocking. Literally. Most of them only come with a PSU, you can't really do much with them.