My take on this: Microsoft is using a free market approach to Google's dumping of Android at a loss in exchange for manufacturer adoption.

Yes, they could try to litigate and pursue trade sanctions - but Viewsonic and the other companies are also Microsoft customers and B2B relationships aren't built that way. Microsoft's strategy is successful because licensing is clearly more certain than litigation and probably cheaper as well. Given that Microsoft leadership has a fiduciary responsibility to protect the companies IP vigorously, their licensing program is as much of win-win solution as is possible under the circumstances.

Determining whether or not reaffirming the cusomer-vendor relationship between Microsoft and the major device manufacturer's is a brilliant move in the long run, is left as an exercise for the reader.