Language change doesn't have to result from a "need" for a new word. It can happen just because ppl choose to use a different word. And the developer of kbin is a Polish speaker. Maybe he chose "magazine" because the Polish word makes more sense to him than "community" (I know about the rifle pun. Wordplay works even better when there are multiple meanings)
Either way, my point is we currently have at least 4 words to describe these things (group, community, magazine, sublemmy). Users will coalesce on one or learn that they're all synonymous and won't even notice when someone uses a different term than they use