Valve has now provided that, 'Content that may violate the rules and standards set forth by Steam's payment processors and related card networks and banks, or internet network providers, in particular, certain kinds of adult-only content' should not be published on Steam.
"[Game-key cards] will start up on the console or system that it is slotted into, so it's not tied to an account or anything," Tetsuya Sasaki, general manager of Nintendo's technology development division, told GameSpot.