Ordering direct is something like 70% cheaper than retailer price. I don't think they need to give more incentive to order direct.
I suspect it's more to do with fairness amongst their growing list of retailers. If BBTS gets their shipment first, then when Nerdzoic gets them a few weeks later, maybe demand is much lower since people got them from BBTS already.
Although in reality, I'd guess this is more about protecting BBTS than the little retailers because BBTS and DS are super slow to ship anything compared to smaller shops like nerdzoic.