Why did apple under-clock the iPhone 3gs' CPU speed from 833MHz to 600MHz?

I have read the tech-specs for the Samsung ARM A8 Cortex Processor, and it says the processor speed is 833MHz. It also stated that it can handle 720p video recording and playback at 30fps. I don't care if it it was for battery purporses. It want REAL answers from Apple. I have the tech-specs photo below. Thanks in advance,

Michael Keith