Yeah that's true, there's also the maintenance burden to consider as well. It would be a pretty big departure for Valve though, Apple was always selling hardware but Valve wants to get their storefront in front of as many people as possible because that's how they print money. They also want to get more folks gaming on Linux so I think the incentives right now line up pretty nicely for Valve to want other devices running their os.

We'll have to wait and see. I personally would love to see more devices running SteamOS as well so I'm definitely biased!