That would hold if they always sold their product at "half-off" what a retailer would sell at. When they aren't having a sale, they are pocketing the money that would have gone to the retailer, too. It's no big deal, since that's what outlet stores are all about, and most manufacturers allow you to buy their stuff online. Example, I saw an Epson photo printer and bought it at a retailer after seeing it and having it recommended by the salesman. Two years later I bought a larger format Epson printer from Epson's online store. The retailer "made" both sales, they just didn't make any money on the second one.

Are retailers doomed? Suprisingly, not yet.