[syslog-ng] why /var/log/syslog, /var/log/messages etc

I would be interested in a link to a document, explaining what is the idea behind log-files like /var/log/syslog and /var/log/messages etc, and why some information is often being written to 2 or more files instead of 1. And why some distros will log DHCP-messages to /var/log/daemon.log, while others will use a different log file. Of course I know that this is all up to myself to decide, but I would like to understand better what is the reasoning behind the various options. Z.