Here's an idea I've been trying to sell to the various reporters that have called me about executive privilege in the last month or so: It's advantageous to each branch to try to position itself as a defendant if the case gets to court, because that way, a judicial decision not to intervene is a de facto victory. For example, suppose that (A) the House were to go to court to try to get an order compelling Harriet Miers to testify, and the President (on behalf of Miers) cited executive privilege. A decision that the case is non-justiciable would be a victory for the White House. On the other hand, suppose that (B) the House Sergeant at Arms seeks to arrest Miers for contempt of Congress, and Miers goes to court for a protective order, citing executive privilege (backed up by the White House). Now a judicial decision not to intervene is a victory for Congress. To be sure, there's nothing technically stopping the House from attempting scenario (B) after failing at scenario (A), but because these matters tend to play out in the court of pubic opinion, that would be much less advantageous than attempting (B) directly.
As I said, I've been trying to sell this "each branch wants to stay on defense in the courts" theory to reporters, but they haven't been biting. For example, this recent Time Magazine story quotes me saying that the courts like to stay out of these disputes, but omits my explanation of how, knowing this fact, the other branches behave strategically. Okay, so I'm publicizing this little theory here.