Gawker tries their best to explain the accents. My friend Meg and I have talked about this exact same issue and tried to parse the accents of the characters.

I disagree with the part about Tyrion (Peter Dinklage).

Peter Dinklage: I mean, I don’t know. A disaster, basically, but somehow it works.

Yes, it’s a disaster. No, I don’t think it works.

Tyrion fanart by Fantasy 2000