Have you thought about the amount of money needed for last year's network hashrate jump and the money needed for next year's jump? It's a big big difference.  Jumping from 150TH/s to 120PH/s is not the same as a jump from 120PH to 3600PH/s. If we assume a 0.5$/GH * 3480PH= 1.74B$ needed for this diff jump. Don't really think that there are so many money that are just waiting to be spent on bitcoin hardware.