Fall? C'mon, they have repulsorlifts! We know that Acclamators (which are pretty large, not as big as Imperial Star Destroyers, but darn huge) can make planetary landings (check out the end of AOTC), as can the "battleships" of the Trade Federation (see Episode I, and also the core ships in Episode II).
So just go into the upper atmosphere and start the bombardment. According to the ROTS novel even, there is only a small shield around the Senate building. You could devestate the planet (and the planet was devestated, if nothing else than from falling debris from the battle, again according to the novel).
Logic dictates they could bombard the planet if they wished.