The assumption is fundamentally invalid because there will always be changes in "available technology". Even once bitcoin mining ASICs reach the cutting edge in terms of modern process size, algorithm optimization, computational efficiency, etc, major companies in larger markets will continue to push the bounds of technology forward and ASIC manufacturers will benefit from these new technologies, releasing better and better products. The cost of a given amount of computing power is cut in half on about a yearly basis. So long as advanced human civilization exists, technology will continue to progress and there will never be a "steady state". And, so long as bitcoin remains valuable enough to warrant anyone to bother mining it with custom equipment, any miner bought at a given point in time will provide less hash rate than a miner bought a year later for the same amount of money. And that makes the graph not applicable in any real situation.

Remember where the discussion originated. I made the claim that even today, many miners fail to ever break even or just barely break even. The graph was posted as a rebuttal to that, to show that in fact capital expenditures are easy to recover and that we are far from the point where that would no longer be the case. But it only shows that in a constant difficulty environment. In a rising difficulty environment, say 10% per period, my statement is closer to the truth, as can be quickly checked with any of the conventional online mining profit calculators. And, said rising difficulty environment is the real world in which miners are trying to make back their investment and profit.