I've heard that too. It's a security feature to protect people from unauthorized photos being snapped. Never bothered me much so I never really looked for a way to silence it.Putting the phone on silent mode usually takes care of this.
From my understanding, this inability to silence it directly stems from a problem with "upskirt" photos that guys were doing in one of the oriental countries. They made it a rule that the shutter sound couldn't be turned off, thus preventing them from spying and such.
I don't know how true that is since phones are sold worldwide, but it's the only explanation I've ever found on the issue.