The difference between the headlines "Brittany Murphy dies" and "Man aged 22 dies in car crash" to me is that I know absolutely nothing about the second person. I don't have a face, a voice, a name and most importantly a personality to associate with the second person. Even if Brittany Murphy didn't know me, at least I had a little insight in her life, making me able to sympathize with her or not. This is usually what makes celebrity deaths more tragic (to a larger group of people) than some random person.
I saw a pretty awful and stupid comment on a news site, a guy commented saying we shouldn't care about white rich celebrities dying when there's so many kids in Africa dying of hunger every day. I don't see how refraining from grieving celebrities will make those kids' situation any better at all. Same as eating up all your food won't make them any less hungry. But I suppose these comments will always be around as long as celebrities keep dying.