The other thing with Soriano and the leadoff spot is this... and it's something Soriano knows and the Cubs brass knows. His production will be severly stunted as he'll likely be seeing a lot less fastballs in another part of the lineup, especially the way the other star Cubs have been playing.
With Soriano in the leadoff role, he is prone to getting those first pitch get me over fastballs that he's great at hitting out of the ballpark, you take him out of that 1 hole and instantly there is no reason for him to see first pitch fastball, or any fastballs for that matter.
Soriano is not very good at breaking pitches, plain and simple. Statistics and pitch f/X back that up, he's never been comfortable with them and tends to swing and miss on a great deal of them. Thus, why would you ever want to move out of the leadoff role or into a slot where you're likely to see a ton of breaking pitches and not many fastballs?