Good point, but in Star Wars, I never noticed good combined arms coordination, except for the surface attack on Hoth (and they even explained why a bombardment from orbit wouldn't work).
I can't think of any good sci-fi example of well-executed combined arms other than the Hoth attack (and even then it was done with a "WW1 Western Front" mindset as they only attacked from one direction and no indirect fires from the surface as a rolling barrage).
To put it simply to those who don't understand that doctrine as we do, Riceball; I wouldn't trust the gunners on the Death Star not to shoot at anything popping out of the trench as the Empire always seemed to consider fighter pilots as expendable, so therefore a "shoot them all down (well, not that odd shaped fighter that Vader is flying) and nobody will ask questions later" doctrine might have been in effect.