I think there is a slight difference in what happened in Madrid and what happened in London even though both incidents were the acts of terroists and lives were lost in both tragic cases.
As I am hearing from a variety of news sources, the terrorist attacks in London were somewhat expected, though of course this does not diminish the tragedy.
Also, though such incidents are not about numbers, in Madrid the number of lives lost was considerably higher than in London. Of course the life of a loved one lost is devastating to family and friends and it matters little that hundreds of lives were lost in Madrid plus hundreds more injured, while in London the number is about 50 lives lost and hundreds injured.
And if you look at the pictures, it's not just Charles and Camilla or the Queen who are smiling, but also the people they are with, whether it be patients, doctors, nurses or others.
I think, as mentioned, it's more important to note that Charles, Camilla and the Queen visited the patiences so soon after the attack. Remember the public outcry when the Queen carried on with her holiday following Diana's death? No hiding for the Queen or any of the other royals this time. She, Charles and Camilla were right on the front lines meeting with those affected by the attack and those aiding in recovery.