Not entirely true. Windows can run into licensing problems from time to time, which you don't get with the other major OSes. Buy a used macbook? OS is fine. Buy a used Windows PC? Well... the vendor said it was genuine. Turns out if you try to get the security updates, it starts complaining about not being genuine. I had to sort out exactly this problem for a nontechnical ex-colleague of mine who'd bought such a PC for her new small business.