Interesting question. I've not really noticed this myself, perhaps because I don't really go back and read the "other threads" people link to. I'm way too lazy for that.
But, I think a good way to handle it, if one feels it's being "thrown" at them by another poster, would be to elucidate why they
think the two threads are in fact different, and then let the other poster say why they think they're similar (or vice versa). One person might feel the differences are superficial, another might feel they're at the core of the issue, and that could be a way to give both people (and everyone reading it) a new perspective on the situation.
But, I admit it would be very frustrating at first, if the similarities or differences seem very self-evident to one person, or if they feel the debate between threads is distracting from the main issue.