I do not for a moment believe that Amys death is of greater significance than the tragic loss of life in Norway. The think is many people knew Amy through her music and the press as well as those who knew her in person. In that way alone her death hits more people than 94+ lives that most of us do not know. All loss of life is tragic but some lives have a greater impact on people than others - Princess Diana for example was just one person but her death brought the country to a virtual standstill.
Its also the case that, for better or worse, the deaths of fellow Britons are always seen as more important than those of other nationalities. It reminds me of a sketch (Not the Nine O'Clock News I think - can't find anything on Google or YouTube) of News for Penguins where the only thing of importance in each news report was whether any penguins were involved/injured/killed. I'm reminded of it every time a disaster is reported with an obligatory comment of whether any Britons were involved as if the rest are of lesser importance.