Additionally, mandatory telemetry was in no part of the purchase process (well, neither were ads). Instead, it's in a completely separate clickwrap 'agreement' (that's subject to change without warning) that's only made clear when you're install the software.

One thing you're omitting: windows xp home was only $199, just like with windows 7. vista seems to be an outlier in terms of prices.

Also, all the prices you've listed are for the full version (ie. not upgrade). The upgrade prices are much lower, and are in line with the current price for windows 10, which does not have separate pricing for upgrade vs full. You can still interpret this as a price drop, but most people get their computers through OEMs, and so aren't paying retail prices. I suspect people who build their own PCs also tend to not buy legitimate licenses. Also, AFAIK the checks for the "upgrade" version aren't particularly rigorous. You could install a pirated copy first, leave it activated, then do a clean install, and it wouldn't complain about the licensing.