This isn't exactly a bug, but submitting a feature suggestion here seems as good a place as any. There is a vital option that IMO should be in logrotate. As it is, the only way I can think of to avoid your logs rotating out of existance is to have them mailed to some account which processes them accordingly. However, IMO having to mail the old logs in order to be able to archive them somehow is a huge kludge. An alternative (not necessary the best one) might be moving it to a directory and renaming it to [logfile].`date +%d.%m.%Y` or something.
You can set a very high number of rotations and get the proper affect. Alternately, a prerotate script could copy the last version of the log to a special directoyr for archival.