Why is the 'has this question already been asked' system so bad?

Question

It came up with a bunch of totally unrelated questions for the above, for example.

Answer 1

If you're referring to the search, not even Google could make sense of a nonsensical search.  If your search terms consist of nothing but words common to just about every single Q&A thread, then you are unlikely to receive a good result.

From just a small test--mostly because there aren't that many Q&A threads at present--the search doesn't immediately jump out as being terrible--unlike, for example, the search on the forums.

Comments

Yeah, but if it can't find something close it should show nothing rather than something wildly inaccurate.  The search should probably be ignoring the common words.

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Your example search used nothing but common words, it couldn't help but to be close to everything.

Which words do you think it should ignore?  I'd probably agree that things like the articles should be filtered out, but what else?  Once you get past very simple words, you're on an extremely slippery slope.

To be clear.  I'm neither defending nor apologizing for the Q&A search--my beef with the search on the forums is well known.  It is likely, however, to be too early to tell whether it sucks or not as there's simply not enough threads to see how well it sorts gems from dross.