Not sure if anybody noticed that logwatch is not reporting any stuff from /var/log/yum.log file. This is due to date format in log file (yum uses standard syslog date format, while logwatch script expects US date format).
It seems that upstream doesn't ship with yum at all, so I guesss the problem was never detected there (and in most likeliness not applicable to it, although the upstream logwatch package does have yum scripts).
The problem can be corrected by either modifying yum to use US date format for the log file, or by modifying logwatch to correctly parse yum.log file using standard date format. Don't have any Fedora Core box handy, so I can't check in what format is Fedora's yum.log file. I guess the best way would be to do whatever Fedora Core does (since that is the closest to the upstream).
Here are some patches against logwatch that correct the issue, assuming Fedora Core uses the same log format as CentOS.
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