Basically, these trades all rely on a few premises:
1. Harrison Barnes has not shown signs of progress. He may become an average, or slightly above average, player. But it would be almost unprecedented to see him become a star, given how bad he is right now. Can anybody point to examples of where a healthy guy puts up a 10 PER in both his freshman and sophomore seasons (after two years of college, too) and becomes a star?
Corollary: If we have to part with one of them and the difference in how other teams value them is not large, it is referable to trade Barnes than Klay, who has shown himself as a guy able to put up 20 points a night on a regular, efficient basis. He has other flaws that significantly hurt his value, obviously, but still, he is more of somebody who can contribute today.
2. The Warriors aren't exactly in win now, but in a win sooner rather than later position certainly. Bogut, Lee, and Dre are all 30 or so, and none of their contracts expire soon. Further, given that the entire franchise is based upon the health of Curry's ankles, we're always going to be in a win-sooner mode.
3. Trading David Lee would give us a shot at the LeBron sweepstakes. I think LeBron cares about winning 7 rings--probably the only thing he could do to be considered greater than Jordan. He has never played with either a good point guard or a good center. The Warriors have one of the best point guards in the league and one of the best centers in the league. At the same time, David Lee is actually very good, and we shouldn't trade him if doing so would torpedo our season.
What's in it for us:
A shot at LeBron--Pierce's contract comes off the books at the end of the year.
In Pierce, a future Hall of Famer, NBA champion who just wills his team to victory, and he is still playing at a high level.
Blatche is a somewhat competent big guy. His PER is highly deceptive because his defense is so bad, but he's a league average guy.
A backup point guard who can manage an offense while Curry gets a breather, letting other guys concentrate more on scoring.
What's in it for them:
With the loss of Brook Lopez, Brooklyn has been reduced to starting the undersized Paul Pierce at the 4. Right now, they're headed for a first round exit against Miami. They need to look towards the future.
Getting a highly touted 21 year old like Harrison Barnes is a way of doing that.
David Lee gives them the size they are desperately lacking right now, if they still care at all about making a (brief) playoff run. He also provides them with a player for the next few years. Because they are so far over the cap line, PP's expiring contract wouldn't help them. Nobody is taking Joe Johnson's awful deal off their hands. Nobody is taking whatever is left of washed up KG off their hands. Nobody is taking Deron off their hands. So might as well get something for Pierce, right?
Afflalo for Barnes (use of the RJ trade exception needed.
Pretty simple--we get the super-sixth man we need, somebody playing at a very high level and works very hard. Orlando gets a guy with a ton of potential and gets more ping pong balls for the lottery.