Have you not heard of VoiceOver? Blind people flock to iPhones, because Apple really cares about acessibility (which makes this all the more puzzling.) I think there was even a WWDC video recently in which one of the segments was about a blind man who used the iPhone to help him navigate.
Just tried it with VoiceOver on, it says "screen unlocked" or something like that. So the lack of the unlock sound has no effect on blind users.
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And all these people saying it is still there on ios 7 GM, please post a video or stop saying it. I'm almost 100% convinced you are mistaking "unlock sound" for "lock sound".