Duh!
It's obviously an inverse exponential function of the time/respect continuum.
I think!
Put very simply, humour is always an attempt to bring balance to the force, if you'll forgive the Jedi-Zen analogy.
Both positive and negative extremes are there to be called upon for inspiration, (either solemnity or indifference), depending on the mood of the individual, like plucking a book or Dvd from a shelf. It could be that some people don't handle death well. It scares them. They tend not to joke about it as it is assumed to be a negative event by definition, rather than simply the shedding of a physical body, (that no longer 'suits' their soul purpose), and a peaceful transition from one state of consciousness to another, as some, including myself believe, after 25 years of serious research into the subject, on and off.
Others, having either denied or resolved any emotional issues surrounding life's most inevitable conclusion, at least on a superficial level, are more inclined to engage in cheeky banter and even this sort of forward planning....
http://forum.ship-of-fools.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=28;t=001807;p=1
In this context, Whitney Houston's untimely demise is considered fair game. To be honest, I thought she'd died of a drug overdose years ago. I know she nearly did several times!
Still, a great loss to those that knew her and all of her fans. I was a mere Pup of only 18 when 'I Wanna Dance With Somebody' was in all the nightclubs so it brings back some fondle mammaries of really big hair!
Another tribute, if you don't mind CJ?
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Finally, this article actually addresses the question Rob!
http://www.viewshound.com/art-culture/2011/5/celebrity-death-jokes-when-is-too-soon-too-soon