When looking through the lens of units shipped, then yeah. This omits the vast amount of current install base, and of course it omits the stupendous amount of non-Genuine installs.
Microsoft's dominance in the desktop/notebook OS has definitely weakened over the past 5 years and will continue to weaken, but not because we choose to include tablets into PC sales numbers, but rather for a collection of reasons surrounding the now prevailing mindset that solutions are no longer Windows platform centric.
Most very large companies persist because they use their various channels of influence to keep the playing field the same, because their whole game is based on it. Eventually the there is so much change that no amount of influence can stop it. Adapt your environment you vs. Adapt to your environment.
