The difference is that that many people died an "unjust" death in two very high profile places in a very high profile way. I would like you to point out 5 such days in the past 365 where 2000 plus people have died within one square city block in under one hour. Such an occurance is actually fairly rare and worth remembering.
Each life is special, each death important to those it touches. These deaths touched many, it is truly that simple.