My understanding was that since they specifically mention that the Defiant and Voyager are the only ships capable of planetary landing AND liftoff then it stands to reason that a big 'ungainly' ship like the Constitution Class wouldn't able to liftoff.
Thruster wash, aerodynamics, structural integrity all come to mind but then I am sure there is some flux capacitor on the ship that negates of all that!
I could definitely live with them making parts on the ground and shipping them into orbit for assembly but then that got me thinking off industrial replicators - why not just have them as part of the orbital dock and just fabricate everything!
I honestly do not think there is enough Canon evidence for it to be honest and it is open to interpretation.