If they're not paying for windows, are they going to pay for your game? Why would you care if it runs on their systems or not? Or are game developers just wanting large numbers of freebie players to keep a network effect going, to keep some paying customers but also to keep competitors out (who'd also have to be catering to non-genuine windows users too?)
In the case of China and Korea, most PC gamers aren't playing at home. The monetization model for computer games in east Asia is the polar opposite of the US and Western Europe. you definitely might care about this market because it's very large (note: negligible console penetration in these markets -- it's mostly mobile, PC or nothing)
They're playing at PC bangs (think lounge/club, where you can hang with friends, eat, smoke, sometimes drink, while playing games... you can even get rooms for the night at larger ones), which usually meter out access via an access card. The PC bang gives the publisher a cut of that revenue based on what the customer played. This is the case not only for MMOs, but also for the usual "box" model where you get the game outright. Instead, you just play the game at a PC bang, and the publisher gets a payment from the bang based on the time spent. In the case of F2P titles, publishers primarily get your money via the micro transaction system.
Even then, publishers don't deal with individual bangs/lounges/arcades, but aggregators. The aggregator provides the management/billing software to the bangs, and the publishers deal with those aggregators to get their revenue. The aggregators have no incentive however to ensure that the version of Windows installed at a bang is legit, but only to ensure that their management/billing software can run to provide that value to the bang operator, and to ensure the bang operator can make money in accordance with publisher agreements.
This data comes from users who _play_ Unity games. Whether they pay for them isn't known, but they definitely play games. That alone can be a desirable thing as you noted (network effects etc.).
It also might be that due to various reasons people there tend to not "buy" software (like OS), but are fine with subscriptions (MMOs are _huge_ in Korea) or IAPs.
