Right, there's two versions of it:
1) New threads as almost a stream of consciousness, ex: Who buys from Target? Who buys from Walmart? Who buys from Amazon? Who buys from Best Buy? - vs - What retailers do you buy from? (especially since there will, by the nature of the topic, be cross talk about other retailers).
2) Starting new threads where clearly there are existing threads that are better place, ex: What oil do you use for your car? What cars have good incentives? Would you buy a Ford or a Chevy? -v- <posting in The Car Thread>
Generally for #2, I suggest in the new thread, that maybe posting in the X thread would be better, and they'd get more eye traffic (and subsequently, more replies), I've even mentioned asking a moderator to move their thread.
#1 is more just a lack of understanding of forum communication practices, usually those threads just trickle off into the no-response-abyss ... but it sounds like the admins would be receptive to consolidating them, things like this are generally noticed more by users since they're not any kind of violation, so I call it a "community consideration", and just help by reporting (but in a positive way).