Is the rule of threes a meta-urban legend?

Roger Ebert died on April 4, 2013. Margaret Thatcher died on April 8, 2013. I have heard the urban legend that celebrities die in threes.

1. Does anyone really believe this? Is it an urban legend that this is an urban legend?
   
2. YES- there was an episode of 30 Rock based on this.
   
3. NO- 30 Rock is FICTION.
   
4. Whenever I've seen ``examples'' of this at least one of the three isn't a celebrity. Are politicians really celebrities? For that matter, are Movie Critics really celebrities (Roger Ebert may qualify but very few others would.)
   
5. The notion of Celebrity is not well defined. People change it to make the rule-of-threes work. Can there be a rigorous definition of celebrity, perhaps based on the indegree of the I"VE HEARD OF THEM directed graph.
   
6. I predict that somebody marginally famous will die in the next few weeks and someone will say its the rule of threes. But will the person who says it be serious? And will the person who dies really be a celebrity (whatever that means)?
   
7. The paradox: there are so many famous people that I haven't heard of most of them.
   

I keep a list of old celebrities (defined as people that I have heard of-- websites of old celebrities have lots of people I never heard of) so that when they die I am NOT one of those saying I thought they were already dead. I noticed this when Dear Abby died: (1) young people asked Whose that? where as older people said I thought she was already dead. Margaret Thatcher and Roger Ebert people seemed to know they were alive.