if Valve isn't selling at a loss to poorer regions then they are simply extracting additional profit from higher-income regions on the assumption that those customers can afford it.

Valve can't sell for a loss the same way ebay can't. Valve simply takes a percentage of the price everytime a game is bought, publishers are in complete control of the price they want to sell. Often, publishers will let Steam automatically set regional pricing based e.g. the American price though.

The way these publishers operate, they will simply set the price at the highest possible value to extract as much as money ad they can from those willing to spend 60+$. Those unwilling or incapable of spending that amount of money, will just buy the game later on a sale. Price skimming has only become more and more prevalent in PC gaming with steam being the "innovator" of frequent sales.