To an extent? That's one real understatement. Only Diablo II of those mentioned has thus far garnered a Mature rating.
Nothing stops them from buying these games (like the people actually sell the games give enough of a damn), and it doesn't mitigate the fact that it has happened. Like little kids have anything better to do, compared to teenagers, who DO have something to do (and whether that be loaf, emo it up, or whatever else is irrelevant).
Marketing != consuming.
Well, technically, there should only be one Mewtwo (and technically, one Arceus). Several legendaries seem to have multiple incarnations, as I've pointed out. Do the D/P lgenedaries have only one incarnation? There seem to be some kind of exception because those Pokemon control Time and Space (iirc).