First, I do agree with your posts, but I do have two comments to specific points. Generally, when one discusses who-influenced-who, I do think it's pointless, since everything influences everything ;-) or not. But what the op does forget mainly is that the Books are first, and now comes the Television series (but the next book will of course be later than season 1,2,3,4? ;-)). So it's rather pointless to discuss the look of the series as they rely on the books as well as our modern viewing point. As my first point shows:
And of course the inevitable complaint about the supposed racism of this fantasy world

I am really tired of such comments, especially if uttered by someone who doesn't even know the books and speaks of the HBO show as if it was not based on them. I suppose there are people who wouldn't stop at criticizing LotR films for not making Aragorn black for the sake of political correctness
Since Westeros is a functional analogue of Western Europe, why should there be any black people around? Were there many black people in medieval France, Germany, or England? No. There were probably none, except an occasional slave brought from overseas as a curiosity. In the books, the only black people in Westeros I know of are Jalabhar Xho, an exile prince from the Summer Isles who is a courtier in the royal court, and Chataya/Alayaya, whores in one of the luxurious brothels in King's Landing. Black-skinned people from the Summer Isles trade with Westeros, but that's about it.
There is no "shame in showing an African face" because there are practically no African faces in the setting. Complaining about that is as pointless as complaining that there are no Eskimos in Indonesia and no Aboriginals in the Arctic.
This might be a slight spoiler here, related to the above, so no story or plot spoilers, not even names, but better safe than sorry.
Other shows that do this in a way more extreme fashion are Merlin and Spartacus. Merlin has black knights and a exotic looking Gwendoline, but it's a rather light-hearted show and to a big part directed at kids. So why not show a bit of variety there, it's educational. (since the true facts on medieval life and the Arthus saga will not be in there in any case, it doesn't matter that this is factually wrong

). With Spartacus, I guess, it's mostly budget question (Polynesian actors are more common in New Zealand than Hollywood

).
But that brings me to my second point, namely that TV is a different medium than books:
BTW, I am a bit disappointed by the appearance of the main characters in HBO's GoT. Martin reiterates throughout the book that the great houses usually have sets of distinct physical traits that distinguish them. Lannisters are all blond and green eyed; Cersei and Jaime are supposed to have hair "of woven gold". Targaryens have silver hair and purple eyes, Baratheons black hair and blue eyes, Tullys are auburn haired, Starks traditionally have dark brown hair and grey eyes, etc. They don't really adhere to it that much in the TV version, which is a shame. Also, they make some characters look too good - I realize it's hard to fully capture the looks of some of the characters, but as good as Dinklage is as Tyrion, he's supposed to be much uglier (later he also gets some pretty nasty scars and other wounds, so I am looking forward how they deal with that).
1) TV series are a visual medium, so what GRRM describes needs to also look good on screen which is not always easy. They tried to give the Targaryen purple eyes (lenses), but they said it just didn't look good enough. But they gave Dany the white hair wig and they made the hair of Jaime's actor look lighter. So there's just a range of what you can do to bring the actor's look and the author's imagination together.
2) Actor's Abilities > Visual Appearance. It's better that they picked Dinklage as Tyrion because he can act very well. Besides how many actors/people do exist that fit the description? TV is a visual medium, but visual also relates to the actors mimics, intonation and manners. For example a post on westeros proposed Kim Kardashian as Arianne, and she would certainly have the looks for it. But the rest? ;-)
In the end it's always both, and I would think that adhering strictly to the overdrawn features of a fantasy world (everyone in a family looks totally alike, Lannisters do not have blond hair, but golden, etc. ...) would make the point of it being fantasy stronger, while I guess, the creators want to emphasize more the drama side of the books as that appeals to a larger audience. So more of a realistic look wanted. And also
3) Hollywood Ugly =/= Ugly Ugly . People want to watch beautiful people on screen, the other ones we can see on the bus daily... ;-)