They already can't make enough to keep up with demand. Inducing more demand at this point doesn't make them any more money.

Why would we assume otherwise? Valve, with all its flaws, is the one mainstream company that I'm aware of that is consumer friendly and has no issues disclosing real metrics.

This makes no sense. Valve can already just advertise the Steam Machine on the homepage, the page that everyone sees when they open Steam. They don't need to manipulate any rankings on the top-sellers list, the page that no ordinary person regularly looks at.