There are a number of reasons, but one might start with the premise you suggest that Han/Leia's romance worked fine "without needless dialogue."
That's simply not true -- Han and Leia have tons of dialogue in ESB and all of it, every single "I'd sooner kiss a wookie!" is building the romance.
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MTHaslett, if every single "I'd just as soon kiss a Wookiee" is moving the plot forward, or revealing character, or "building the romance" then it wouldn't classify as "needless", would it?
By needless I mean superfluous - beating us over the head with information we already know or simply stating the obvious. One of the most important rules of writing screenplays is that you don't tell when you can show.
The point I was trying to make is that ESB is never dragged down by redundant, expository, non-entertaining dialogue. Han never turned to Chewbacca and said "I haven't see her since she gave me that medal on Yavin IV after we helped Luke blow up the Death Star, Chewie. I've thought about her every day since we parted, but... She's forgotten me completely."
THAT dialogue, in my opinion, certainly falls into the "needless" category, the likes of which AOTC and TPM are rife with.
Good romantic dialogue: "We need? ... What about you need?"
"I need? ... I don't know what you're talking about."
"Probably don't."
Bad romantic dialogue: "Believe me, I wish that I could just wish away my feelings, but I can't."
"I will not give into this. If you follow your thoughts through to conclusion you will find they take us to a place we cannot go."
First of all, is Natalie Portman capable of using a contraction? Or is she one of the Stepford Wives? Secondly, has George Lucas forgotten the words sub-text, insinuation, innuendo, allusion, overtone, undercurrent? The only scene in AOTC which I felt really accomplished this at a level even close to the OT is the scene between Jango and Obi-Wan on Kamino. For some reason, that scene always makes me think of Cloud City.
Anyway, my idea of having Anakin and Padme already be lovers at the start would be a challenge to pull off successfully, and you're probably right about it, MTH. From reading your posts, I think you have a pretty good sensibility about these sorts of things and I usually find myself agreeing with you. I would, however, eventually like to see someone try to make it work.
I like the points you brought up about the pacing of the duel. It would definitely make Dooku seem more malevolent than he originally came across, which would be a very helpful addition to his character at that point in the story. But, one thing that concerns me is your suggestion to cut Padme out of the final scenes of the film. While I agree it distracts from what we should be focused on at that particular moment, what alternative are you offering? She falls off the ship, and boom, next time we see her they're getting married?
Respectfully,
--InfoDroid