Thats the beginners mistake, as long as difficulty increases you will have a decline. And 20PH for 108M? Now, lemme se, where do you get 20PH for $108M? Or 20GH for $108, or 0.18GH/$ or 5.55$/GH.
Yeah, thats what you get on pre orders. And checking mining calculators like genesisblock those devices might, or might not, ROI. And given that current devices, and lets face it, 90%+ of current hasing power comes from asics, the devices in use currently are mostly first gen asics. Only the early orders are gonna ROI. Quite a couple of people are gonna have to pay for the privilege of mining.
But thats actually pretty irrelevant, since the mining industy will obviously converge towards the profit generated from mining. If mining equipment generates money out of nothing you buy it. If it generates less than you pay for it, you dont. The only mining equipment that still has a chance of profiting is pre orders, which is basicly the same as gambling. The size of the hardware mining industy is pretty excactly the same as the profit generated from mining. Yes, things are that simple at times.