It was my understanding that the material in impact bits is actually a softer metal than that those in regular ones (at least that's the case in automotive socket sets). The primary idea being when an impact bit breaks, it doesn't explode the way a harder metal would. Not sure if it applies in this case, but I thought I'd throw it out there...
This is absolutely true, however there is more. When an "impact" comes out of the tools connection point and into the bit/socket, the black metal they are made out of actually has a spring effect, in that if you could look at a super slow-mo of one being used, you would see a wave moving through the socket/bit to the fastener. Standard sockets/bits are actually stiffer and harder, to avoid wear and provide positive transfer of power. Thus regular sockets can literally explode from the instantaneous forces coming from an impact. Usually impact-rated accessories do not fail in this drastic manner, and not as quickly.
