Based on their merits?
The Windows API is so broad, so deep, and so functional that most ISVs would be crazy not to use it. And it is so deeply embedded in the source code of many Windows apps that there is a huge switching cost to using a different operating system instead...
It is this switching cost that has given the customers the patience to stick with Windows through all our mistakes, our buggy drivers, our high TCO, our lack of a sexy vision at times, and many other difficulties [...] Customers constantly evaluate other desktop platforms, [but] it would be so much work to move over that they hope we just improve Windows rather than force them to move.
In short, without this exclusive franchise called the Windows API, we would have been dead a long time ago.
In 2002, Be Inc. sued  Microsoft claiming that Hitachi had been dissuaded from selling PCs loaded with BeOS, and that Compaq had been pressured to not market an Internet appliance in partnership with Be. BeOS also claimed that Microsoft acted to artificially depress Be Inc's IPO. The case was eventually settled out of court with no admission of liability on Microsoft's part.