Probably was talking about limits for 4 DR sticks. These are more difficult to drive, so motherboard vendors are being very cautious about supported speeds.I heard it in a Jayz2cent vid so maybe he mispoke or I heard it wrong and he actually ment 4600mhz. Did seem odd at the time so I will have to check at some point.
But this only comes into play at 128GB+ memory configurations.