[CentOS] World Writable Files

I'm curious.  Why are so many system-generated files world-writable?  On my 
Mandriva laptop, every day I get warnings that world-writable files are found 
in /tmp, /far/lib/ /var/run/ and /var/spool, and every day msec reports that 
it has changed the mode of several files in /var/log/.  Why are they created 
like that?

Anne
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