I think they add a little more juice for stability. For example, ASUS mobos overvolt RAM too as well as slightly OC the FSB. Right now I got a Gigabyte mobo and it way undervolts everything. The default Vcore is 1.7, actual ranges from 1.69 down to 1.63 or even lower under heavy use. I don't think it should make you worry, it's pretty normal.