Duke, that theory is use by journalists when they have to justify themselves.
Almost every week, especially on Friday, someone says on twitter that has seen them somewhere. If these comments are common ... more will be if the press on the other side is saying they do not do things together.
It happened in May, the prince was photographed in Mallorca with friends, the press began to create a story that he was alone, Letizia hated Mallorca... and the people rebelled against the information in Internet because they had seen the family. Until a journalist posted a picture on twitter on the return flight, the press refused to investigate or tell the truth.
Although rumors had already begun, the Prince went skiing and the Princess to a concert of Felipe´s friend. The day before they had been to the opera with Barroso ... Queen Sofia never goes to the opera or a concert without the official photograph ... of them there was no photo. It would have been very easy to stop rumors canceling the trip of the prince that was private or posting photos of the opera that could be an official event.
Thursday was the birthday of the Prince, and Friday the girls had no school... would be very strange that they had not done anything, when they always do. Their attitude, the way they usually organize their private activities remain the same ... is the press who says it or hide it at convenience.