98 of the top 100 fastest supercomputers in the world run Linux. Most phones also run Linux. See also consumer electronics of all kinds - TVs, routers, webcams, consumer NAS drives ... Linux works everywhere. As Linux has been installed everywhere over the last few years, Microsoft has gone from a monopoly, the 800 pound gorilla, to trying to catch up in order to survive.
There is a reason for this. Linux didn't make any assumptions about what hardware people were going to use next week. Even the architecture could be whatever you anted that day - DEC Alpha, Blackfin, ARM (any), Atmel AVR, TMS320, 68k, PA-RISC, H8, IBM Z, x86, assorted MIPS, Power, Sparc, and many others.
Microsoft built specifically for the desktop, and supported one platform - x86. Suddenly, most new processors being sold were ARM, and screens shrank from 23" to 4". Microsoft could only scramble and try to come up with something, anything tat would run on the newly popular ARM processors, and ended up with Windows RT. Linux kept chugging along because they had never made any assumptions about the hardware in first place. To start maing those assumptions now would be stupid.
We don't know whether smart watches will be all the rage next year, or if cloud computing wll take off even more than it has, or virtualization, or a resurgence of local computing with power, battery-friendly APUs and roll-up displays. To specialize for "dektop" hardware or "server" hardware would be dumb, because we don't know what those are going to look like five years from now, or if either will be a major category. How many people here remember building web sites for WebTV? How well did that pay off, investing in building a WebTV version, then a Playstation version? The sites that faired these changes the best built fluid, adaptive sites that don't CARE what kind of client is being used to view them - they just work, without being tailored to any specific stereotype of some users.