I think you are underestimating the salaries in other "developed" countries, but you are right that US salaries are much higher than any other country (especially in Silicon Valley)
You have a valid point in that many HN commentators seem to live in a bubble where spending thousands of dollars on a developer for "convenience" is seen as a no-brainer. They often work in companies that don't make a profit, but are funded by huge VC investments. I don't blame them, as it is a valid choice given the circumstances. If you have the money, why not? But they may start thinking differently if the flow of VC money slows down.
It's similar to how some wealthy people buy a private jet. Their time is valuable, and the cost seems justified (at least if you don’t care about the environmental impact).
I believe that frugality is actually the default mode of business, but many companies in SV are protected from the consequences by the VCs.