Well, obviously all PCs are Steamboxes, technically speaking. However, if it's a streamlined box that plugs right into a television and boots right to steam, I could maybe see them putting up a stink, even if the branding was sufficiently ambiguous.

The MistBox ;)

I don't know, though. To be honest, I'm kind of shocked no one has tried this yet. It seems like such an obvious winner, even if there is a slight chance you would go to court with Valve.