Operating cashflow and depreciation curves are the most basic accounting principles out there, the author did not make anything up - he is applying a logical analysis to publicly available data.
If someone were to talk to you about the cost of printing and distributing books and how much X costs and depreciation over 10 years, you as an ebook seller would laugh them out of the room. Sure there are things that still apply across all businesses, but people seen to dance around the fact that the reason why depreciation model does not work for bitcoin mining is that it's highly correlated to advances that were made in the mining hardware + the huge role the cost of power (geographical location in the end) has on the whole profitability of things.
Mining needs hardware, which loses value as new hardware is released and mining gets harder. Thus, it depreciates over time.
Exactly, that's the whole point of the article.