That is my point, though: it wouldn't have happened. But it did for Homer. Apparently either GRRM is in respect to maintaining authenticity more important than Homer, OR (maybe a tad more likely the case ^_^ ) it is easier to polititroll with some shows than it is for others. I am sure you can imagine that GoT would have faced serious problems if black Lannister protagonists were there.
It didn't happen with GoT because HBO wouldn't risk their show facing problems due to some strange casting decision re protagonists. Let alone that GoT was a serious production, unlike Bbc's 2-years-in-the-making terribly bad fiasco* which is ranked among the worst in IMDB :o
*goes without saying that after the show aired it became apparent it is garbage and would still be garbage even without the terrible casting. But this might be accounting a bit for the casting done as possible diversion (?), given the show took so long to actually produce a first trailer or other info.