It turns out that I was mistaken about the DVD set of the Two Towers - the 4-DVD set has completely different special features from the 2 DVD set. Wow. I have a lot of watching to do!
One thing that I wish had been duplicated is "Gollum's Song" - it isn't on the 4-DVD set at all! The horror! Now I have to go buy the other one too. Evil merchandiserssss. I hates them! I hates them forever!