So in the case of the hummingbird most people think this cpu can actually top out around 1.6Ghz. We will likely need 1400-1450mV for that speed though. The danger of course of pushing the edge is if you push too far you fall off. So even if Samsung has a cpu capable of say 1.5Ghz on 1400mV thats too close to the edge. Too likely to burn out, fry, get unstable and have Force Closes for apps. So they back is down and off, way off. Its kinda like a car and the redline. Lets say my Honda Accord redlines at 6500rpm with a top speed of 135mph. If I always drove it at the redline rpm and at 135mph Im going to burn out the engine a lot faster than if I run it at 80mph and 4000rpm. So bottom line they will put out the cpu undervolted and underclocked mostly for longevity and reliability sake.
Sorry for the length of this geez; I got on my soapbox there