If I went ahead and said "I'm glad they're dead" then yes I would be a troll! But I don't.
I can only really think of 1 person who I wish was dead, and I'd be just as happy if his band split up instead.
Not to get all Nick Hornby, but I think this started with the reaction to Princess Diana's death. My Mum actually took a train from Yorkshire to London to look at the flowers outside St James's Palace. It actually seemed like a reasonable thing to do at the time, if she'd done the same for Jill Dando, we'd have been worried about her mental health.
24-hour news channels have a lot of time to fill too, so the reporting of every event is not complete until we've:
a) Watched footage of people leaving flowers outside a football ground / hospital / makeshift shrine
b) Seen an endless rolling feed of related tweets
c) Heard what One Direction's view on the matter is
You can't blame them entirely, it's a very easy way of padding out a news story, but I don't think it adds to our understanding of an event to read:
"CARNT BELIEVE HIS GONE- MISS YUO MJ XXXxX"
scrolling along the bottom of the screen.
This is officially a tangent now isn't it? Rant mode off.