Because it's fun!

"80% of the crashes are resolved by fixing the top 20% of the bugs", ~Microsoft.

More from the wiki:
20% of the code is responsible for 80% of the results
80% of the resources are typically used by 20% of the operations

I think that 20% of the game developers create 80% of the games.
What do you think?

20% of the active forum users posted 80% of the posts?

really, it has unlimited uses. I'd like to see exactly how accurate it is tested in various situations.

http://en.wikipedia.org/wiki/1%25_rule_%28Internet_culture%29

there you go