If you haven't watched The Wire yet, this clip gives you a good idea of what you're missing: [youtube]7bR3T1eThJU[/youtube]
It's amazing writing. The metaphor for the whole series is delivered in three minutes. And the motto "the king stay the king" applies not just to drug dealers but to every institution in the show. Whatever the characters do, however hard they try to effect change, everything stays the same.
But like all great writing, it doesn't just advance the plot, it reveals character too. D'Angelo knows the rules, so we know he's too smart for the game - smart enough to know that a pawn can never win. Wallace, on the left, is ignorant of the rules and doesn't really understand them, even when they're explained to him. Bodie, on the right, is ignorant too but arrogant enough to think that he can win. He can be the pawn that makes it.
The important point to remember is that scenes like this are the norm in The Wire. It's all written like this: rich, thoughtful and powerful. There's more to say about this scene but stop here if you haven't reached the end of series four.
Of course, by the end of series four, all three are dead. Wallace and D'Angelo died trying to get out of the game and Bodie died trying to stay in. In retrospect their fates were obvious from this scene. The writers probably knew how Wallace's story would end when they wrote this scene. They may have known what would happen to D'Angelo. But there is no way Bodie's fate was decided when this scene was written.
It just shows the extent to which the writing on The Wire serves the needs of the characters.