He was talking about Episode I, which featured no shielded Coruscant. Think gungans... In other SW movies, such as Episode V, shields are not penetrable by slow objects (like drop ships).
I believe Empire Strikes Back is more appropriate.
"Lord Vader, the rebel base is protected by a deflector shield. It is strong enough to resist any bombardment"
"General Veers. Prepare your men for a surface attack"
Basically I think you can't cover the entire planet unless you are a galactic level civilisation. Do what the empire did, land armour a few kilometers away and attack via land.