When folksonmies were the current hotness Clay Shirkey made a great point about things that seem similar but aren't.
"Synonym control is not as wonderful as is often supposed, because synonyms often aren’t. Even closely related terms like movies, films, flicks, and cinema cannot be trivally collapsed into a single word without loss of meaning, and of social context. (You’d rather have a Drain-O® colonic than spend an evening with people who care about cinema.) So the question of controlled vocabularies has a lot to do with the value gained vs. lost in such a collapse. I am predicting that, as with the earlier arc of knowledge management, the question of meaningful markup is going to move away from canonical and a priori to contextual and a posteriori value."
This is a false analogy. We're talking about identical content (a particular website) as compared to two different linguistic terms. The point about folksonomies is interesting in valid in its own right, but should not be used as a justification for duplications on News.YC.
"Synonym control is not as wonderful as is often supposed, because synonyms often aren’t. Even closely related terms like movies, films, flicks, and cinema cannot be trivally collapsed into a single word without loss of meaning, and of social context. (You’d rather have a Drain-O® colonic than spend an evening with people who care about cinema.) So the question of controlled vocabularies has a lot to do with the value gained vs. lost in such a collapse. I am predicting that, as with the earlier arc of knowledge management, the question of meaningful markup is going to move away from canonical and a priori to contextual and a posteriori value."
http://many.corante.com/archives/2004/08/25/folksonomy.php
I think this can apply to anything where similarity can seem like a problem.
Just because items seem simliar doesn't take into account the context in which said items are used.