Alright, now factor into that the average cost of 1TH. Four years ago 1TH cost a couple thousand bucks, now it's about $100. I bet the graph gets a lot flatter if you normalize against that.
Absolutely! Hardware has also gotten more energy efficient. The graph makes no allowance for any kind of expense, but neither did the OP's question (if I read it correctly). I just tried to answer the question in the same terms it was asked.