Some of the reasons for the success of the Chromebook are clear. For example, they can cost 1/10 the price of a MacBook--that's pretty compelling. Also, Google just announced at I/O that Chrome O/S will now run apps from the massive Google Play app store. Chromebooks are simple, affordable, and getting even more flexible. They're doing extremely well in the education market and they're leveaging that success into other sectors.
I've been a long time fan of the Chromebook. In 2014, I blogged about Why I Just Bought a Chromebook and then followed up with another post reviewing the Toshiba Chromebook that I'm still using today. As a Chromebook user, I'm not surprised that lots of people chose Chromebooks over the alternatives, but that doesn't make the news any less impactful. I'm sure that a random poll of people on the streets would not place Google anywhere near Apple in computer sales.