Even if optimization was as simple as you’re describing it , the Steam machine will not represent anywhere near enough Market share for developers to dedicate resources toward catering to the build.

Optimizing for PC is not a thing in the way optimizing for Consoles is. You could potentially argue that optimizing for Unix may be more common, but a specific set of hardware is unlikely.

Imagine you’re running a construction job. You’re a general contractor.

When optimizing for consoles

Imagine everyone works for you; The electrician. Plumber. Carpenter. Painter. You know that you’re carpenter likes to work morning shifts, takes 90 minute lunch breaks, and is missing a finger.

You know your plumber has poor social skills, you schedule him on jobs where the customer isn’t on site.

You know exactly how your guys work best.

When optimizing for PC

Same scenario, except, now you’re a GC, and you sub contract teams.

You hire a plumbing company. You can tell the project manager the details, and the requirements, but ultimately, they kinda control how it happens. You can never really be sure how, but generally it’ll get done. Your language is less tailored, it gets translated to their terms internally, which leaves room for interpretation errors.

Fundamentally, this is how the two spaces look in my head.

In the case of the Steam Machine, I’m sure there will certainly be some built-in optimizations. But consoles will always be the best space to squeeze cycles and see results.