If they were fighting a war to demoralize the people, I couldn't think of any way better to do it then to destroy national icons. Also, did they yet to raze the Kremlin at all? Did the Americans try to bomb the inertial palace? if I recall right, all the nations avoided national landmarks (excluding the Siege of Berlin)
Firstly, Buckingham Palace was hit by bombs quite a few times during the Blitz, as you can see here: http://bombsight.org/#16/51.5011/-0.1428
However, that's not to say that it was bombed deliberately. You're making an assumption that they could, in fact, bomb with sufficient accuracy to target landmarks. The Germans generally bombed at night, and partly because of British blackout procedures were unable to rely on visual bombing. Their guidance mechanisms, in brief, consisted of two radio beams from widely spaced transmitters which crossed over the target. Bombers would follow one of these beams, and when they intersected the other, they would drop their bombs. This was generally accurate enough to get them over the city they were heading for, but it would have been essentially impossible to have beams that were tight enough and aimed accurately enough to place bombs on a target of that size, especially not while under antiaircraft fire and attack by fighter planes.