This is true but it's not going to happen that quickly. Traditional computers are still where "serious" work like homework is done. In my experience anyone who does more than spend time looking up recipes and checking out Facebook considers their phone to be too limited for "real" work.
Some people might be happy with a bluetooth keyboard and a tablet but clearly the billions of dollars in sales of traditional PC hardware shows that the desktop is here to stay for a while.
My point, basically, is that no one is going to look back at history and say "Microsoft purchasing Nokia's phone division was the end of the desktop PC." They're going to look at the release of the iPhone and then the time that Android, iOS, Win Phone, etc became just as good (i.e. no one thinks "should I use my iPhoneLapDocTop or my Windows Laptop") for general purpose computing as Windows and OS X every were. I think cloud services and "dockable" phones with proper large screen UI/UX will be key to that. I'm pretty excited about that, assuming it happens, as I sometimes find my MBPr too large but my iPad too limited for some things like interviewing potential hires. Using the same core for each would be very handy, but I've digressed.
Also don't discount those holdouts. The fact that Windows gained so much of a foothold in the home because it was what people are/were using in the office. The Mac OS, even if it was 100 times better that Windows at any given time didn't have that ubiquity. Smart phones have the benefit of being in everyone's pocket, but until your boss/HR sets you up with a brand new iAndroidPhone OS laptop for work Windows will still have that crutch to lean on.
IMO the patient is terminal but the prognosis is a drawn out death that might be lived on by Windows Phone if any of this works out.