[toyg]

>"is this machine actually capable of running this game?" check. Non-trivial to implement, sure,

Quite trivial, actually. They already do the necessary data-gathering at your end (i.e. their periodic automated survey), the only "hard" bit is data-gathering at the other end (when a game is listed).

It's so trivial to implement, in fact, that one has to wonder whether there are commercial considerations overriding the technical aspect. Maybe they don't want to piss off hardware and game vendors, maybe Valve would rather have you buy their console to bypass these considerations altogether... who knows.