IF you are only interested in the main topic, then this other related topics table doesn't matter. The question comes, when you DO want to use this table, are you normally going to want to include the main topic in the results or not. Generally for this sort of thing, most of the time you want the main topic included, and the cases where you want it excluded, you are also for the operation getting the main topic, so removing it from the other related topics isn't hard to do.