Gunsmoke can sell the upper cheaper, Keislers may even have them (again at a discount). This is nothing new. Bushmaster sells at MSRP. This allows their dealers to sell for less (by buying bulk themselves or from a wholesaler who purchased in bulk). If the factory always undercut the dealers then there would be no incentive for the dealers to carry the product.
This is a VERY common situation with manufactured items.
I picked up a BM M4 uper from Keisler's and saved about $80 off of Bushmaster's price. And the shipping was less than half than BM and arrived only 5 days from date of the order. Gunsmoke's prices are also good.