"wildly successful Lumia 520"?
Anyone got numbers for that? As far as I know, Microsoft and Nokia do not release figures for individual phones, but only an aggregate number. According to http://blog.adduplex.com/2013/08/adduplex-windows-phone-statistics.html the 520 has almost 30% of "the market". The market in question is the Windows Phone 8 market. The same site says the 520 has 18% of the "Windows Phone market", which is a figure we can use. 2013 data can be found here:
Windows Phone has 3% of the smart phone market, so the market share for the 520 is 0.54%. Microsoft accounting gives Linux 1.5% of "the market" (They might mean the pre-installed OS on desktop and laptop computers but never actually say). With tripple the market share, Linux on the desktop must be spectacularly successful.
If I was feeling particularly cruel, I would ask how profitable the Lumia 520 was.