The idea is because your time is more valuable. I'm not sure I agree with a Mac having a lower total cost of ownership in either cost or time, but that's the idea. Don't do work Apple pays Chinese laborers to do.
I had an IBM laptop before I had a Mac. At least one major component had to be replaced every single year for the duration of the four years I had it. Keys broke. the screen was shite. Windows crashed constantly. I lost all my files multiple times. After having it for more than a year it ran as if someone had permanently applied the brakes and it was just grinding against them and no amount of service seemed to be able to fix this. I spent weeks searching for the specific charger I needed only for the company to ship the wrong one, then when I had to replace it a second time they no longer manufactured it so I had to buy one second hand. That machine was an utter sinkhole of money and time. I swore off Windows products that day and have not spent a dime on them since. Maybe things have gotten better since XP but I'm not about to risk it.
Now I have a Mac. I have had the same MBP for 6+ years and it has never once required service, it runs perfectly, has never lost data, and has been a charm to work with. Sure, it cost me 2x as much as the IBM but in cumulative costs that is nothing. I could easily see this laptop lasting me another year at least.
I am not saying you are wrong, just providing my experience in which the cost of ownership in money and time has in fact been lower.
I don't need to reinstall the OS or download an uninstaller to remove bloatware. I don't need to install antivirus (yeah, this one isn't required, but the reality is that there is much more malware targeting Windows). I don't need to wait for Windows Update to finish before my computer shuts down or boots up - these are particularly painful. I don't need to worry about programs scaling to a retina/high DPI display. I don't need to spend time reading articles about how Windows 10 is tracking me and how to prevent it. I don't need to worry about my laptop breaking, because if it does, I'm a genius bar appointment away from getting it fixed. If my Samsung laptop breaks, I need to ship the whole thing, likely wasting weeks.
Not everyone experiences these issues, but this is how it feels for me. I made a very gradual transition to OS X - owning PCs, building PCs, using OS X on my PCs for almost a decade, then finally buying a Retina Macbook Pro.
While some of your points are valid for *nix setups as well (in terms of hardware, etc.) you've implicitly made the assumption that the only alternative to OS X is Windows, which strikes me as somewhat off base in a place like HN.