I'm interested to hear responses to this too.
We can't be perfect all the time. Queries sometimes get lost amongst the wealth of mails we receive - we know they shouldn't, but occasionally they do. We try to give constructive feedback, or at least a reason why we have rejected a story, but it's not our intention to upset anyone so sometimes it's best not to say too much.
And I also wonder why you were wondering. Have we failed to respond to a query? No one should fear a rejection and you might just hit the happy, quick-responding phase of our Mercurialism.