My original point still stands that Renly played the game much better than Stannis. Stannis sucked at the game and continues to suck at it. That's why he does something all together different in the third book, because he got his ass kicked at playing it at the end of ACOK/Season 2. He only got as far as Blackwater Bay because he used magic. Without magic, he'd be left to his own devices of winning through politics and cunning.....and he'd have been sent to the Wall a long time ago at this point in the books.
You say execution, I say murder. Otherwise, you should think the entire Stark family deserves execution for they do not recognize Stannis either. And Robert and Stannis should have both been executed for rebelling against the Targaryens. To hide behind fratricide, a crime beyond the laws of men in most cultures, by saying it was "an execution" is weak.
Just my opinion.