Every website I've seen that publishes stats, chrome books amount of a portion of a single percent of clients viewing them. Assuming people buying Chromebooks are in fact hooking the up to the net (and if they aren't, what are they doing with them?) that suggests the idea that massive drop in the number of windows licences is not, in fact due to Chromebooks.
In fact, let me put it this way..
Windows sales down. Chromebook sales : A few thousand a month. Tablet sales (including all flavours that don't require a windows licence) : several million a month.
Headline : "windows sales are dropping because people are buying Chromebooks!"
I refer the reader, as I often do, to
Betteridges Law. To quote the man himself..