Well, unfortunately, locking a topic isn't an exact science and it's also not a decision that's always reached easily. Most often than not, OT topics are cleared if they somehow relate to a DS actor, they directly relate in some way to something special in the topic starter's life, or they at least relate in some way to the horror genre of which DS is itself a part. For example, the topic about the Best Buy sale highlighted horror films which might have been of interest to DS fans, the topic about the passing of Robert Earl Jones is connected to Grayson Hall as he played her butler on OLTL, and the topic about the Golden Girls book in part highlights that the topic starter was interviewed in the book. (Truthfully, if it hadn't been for that personal connection in the GG topic, it wouldn't have been locked, it would have been pulled from the board outright because it would have had no relationship to DS at all, not even tangentially. Hundreds of such topics have been pulled over the years, most often before most members were even aware that they had ever been posted.) As Midnite pointed out, the original Star Trek series is a contemporary of DS, so several DS fans might be interested in the info shared, and so that's why it was left on the board - however, any further discussion of the shared info was better suited for an ST forum.
I hope that explains the situation a little better.