Netbooks were a cheaper product, too. Tell me how well the netbook is doing today in comparison to everything else? In case you didn't know, they rose high and fell hard.
Also, it's obvious you haven't USED Windows in the past 18 or so years if you think it hasn't changed much. It's also obvious since you talk about defragmentation, call it "crash", mention that it has to update constantly (1-2 times a month is not constantly), and then mention the registry as if it means something.
If Windows is dead, what does that say about every other OS that doesn't have 1.5 billion users?
Netbooks sucked though, and Chromebooks don't. I'm not saying Windows' marketshare is dead, I'm saying the platform is dead. The marketshare is arguably dead too, because it's certainly not growing, but I'll leave that to you to decide.
Here's the part you're not expecting though: I'm still a Windows guy. I'm a platform polyglot. I use everything.
I have a custom built workstation running Windows 7 that was originally a gaming machine but has since been converted. I'm building another desktop, possibly for Windows 9, though most likely for Linux. I used Windows Vista and before that my first laptop ran Windows XP.
So, coming from a guy who still uses Windows every day, and a power user at that, the Windows platform is dead. Every week I have to install between 5-20 updates, I get an infection regularly (around every 18 months is my average), I have to defrag my hard drive, fix registry errors, wonder why the entire thing is slowing to a halt, etc.
I'm sick of it. I've been dealing with it for 10 years, and that's enough. I don't have to do ANY of that crap in OS X, (I've never run a maintenance program. Ever.) and as a whole, the UI is easier to use.
It's also more stable, I've never once had a kernel panic. My Windows 7 machine, on the other hand, crashes nearly once every three weeks. It is admittedly getting old, but again, I've never even seen a Mac crash once.
I also dual boot Windows 8.1 on my laptop, because I had to start developing in a beast called LabVIEW a few months back. It sucks even harder, because I still have all of the annoyances and instability of Windows 7 and under, but on top of that, I have to learn a new interface that is poorly designed for desktop use? No, I'm sorry, that's [bull excrement]. You can't just reskin a product and act like it fixes all of the issues of your previous products.
Using Windows feels like living in 1999 for all eternity, with the amount of maintenance I have to do. Not even any of the BSDs I run require that much maintenance, (they don't require anything, actually, funny how that works) and OpenBSD is run by a bunch of Canadian buttholes who don't give two craps about usability.
/rant
Thanks for reading the tome of a tortured Windows user, and please have a nice evening.