The problem is that since they seem to be pricing this model in USD, the cost of the units in BTC will fluctuate. For potential buyers that use BTC for their ROI guesswork (like me), fluctuations in the fiat value of BTC can affect the value proposition of the product. Plus a low fiat value of BTC means potentiality a longer ROI, or no ROI, in pure BTC terms.

Compare this to the S2 S3, which was priced in BTC. Sure people bitched about the price when it didn't go down between batches (because BTC's fiat value was going down), but at least you could look at a batch knowing the actual price, do your calculations, and decide whether to buy or not without having to worry that the ROI equation in BTC terms would change by the time you pulled the trigger.

My gut feeling is that Bitmain's careful calculations to sell a product that can just barely ROI (with them keeping the rest of the profits) have been thrown off by BTC's price tanking at an inconvenient time. They want to make a profit, clearly. But if this unit costs too much in BTC, it might not be as competitive as other products, and experienced buyers may pass on the purchase (he says, expecting the usual onslaught of "people on this forum will buy anything regardless of logic").