It shouldn't. Performance testing for the past who knows how many months has probably had them bouncing way up above this and back down and they settled on a clock speed that probably barely affected heat and sound at all(Albert said its all about max speed at a certain maintainable fan speed/sound level). So if the cooling can keep 100% CPU usage at 45 degrees at two different speeds, why would you not choose the faster speed?
This is a SOFTWARE tuning, they are flashing the hardware with a higher clock setting because they are confident the CPU won't fail.
Obviously, there is some risk if a chip is designed for a specific frequency and you tune it higher afterwards. It may break - but if they do that to all devices, I think they are confident enough... or they risk a fiasco.
The massive heatsink they showed off on the E3 demo units should easily allow for a small clock speed bump like this. The fact that they designed the XBO to be oriented only horizontally should allow them to maximize the cooling for that orientation, so I don't see heat being an issue this time around.
Was wondering if this was coming or not. Seeing how big the heatsink is, I figured they would look into trying to up the clock. However, I wonder how long this has been in the books for. If they want to keep their release day close to Sony's, it doesn't bode well if they're still making changes this late... so hopefully this has been kept under wraps for awhile.