actually in the originals they make that clear, but prior to the empire they weren't, the only reason they were after the empire is they had to be careful as the rebels had a lot of things going on, so they had to fool ppl about there ties. also the other reason itd be good is because the castle the tactics invloved, but unlike a place like naboo, alderaan has a lot of open area too, where as naboo is just like a maze
About tarkin he would not have mentioned it, because why would he be thinking about 20 years ago at the birth of the empire, he was more concerned with the way vader disapproved of a lot of what he was doing and how he hired people that kept disobeying orders(at least in vaders eyes, vader just needed a reason to kill his own men)