Maybe because it's not old and still true?
Windows IS unstable, especially Vista.
Of course, Modern OS's don't have stability issues, and that's why Windows is NOT a modern OS.
It IS the OS fault if you're working with perfectly working, powerful hardware and common software and you still get affected by Windows's instability.
BS. A well maintained Windows machine with Vista or XP and proper hardware drivers is not unstable in any way. I've used Vista for several hours daily since January 2007, and whatever stability issues there were initially got sorted within a 3-month window once hardware manufacturers got the hang of Vista's new driver model. Had it been unstable I simply wouldn't have used it, these are my work machines that have to bring in $$$ for me 24-7 and I can't be arsed to waste time troubleshooting.
OS X can feign stability pretty well thanks to the fact that the hardware, the OS and much of the popular software all comes from a single manufacturer. It lives inside the Apple bubble. But this bubble is very easy to pop, and then the boy in the bubble dies because he has no skin. Some innocent third party add-on like DivX or Logitech Control Center whatever can grind a Mac to a halt. How many people did
not get the Mac rendition of Blue Screen of Death when they installed Leopard? What was it this time, DivX, RAID, LCC, Kaleidoscope...? Aww, one little germ sneaks into the bubble and whammo, instant death. Try killing a Windows PC with a weapon as feeble as DivX and see what happens. Hint: Nothing that'll make it freeze on bootup...
As for "modern OS", I wonder when OS X will get network capabilities from this side of the year 2000?
Let's consider this case scenario. You're two people in a home, you have one computer each, one portable mp3 player each, and a NAS drive with gigs of music files on it.
If both computers are Vista or Win7 machines, the setup is a breeze. Both machines will detect the NAS drive automatically, and you can use "Map to network drive" so that the computers will mount the NAS drive permanently. For all intents and purposes the NAS will be treated like a local drive. Right, so then you point Windows Media Player to the folder on the NAS drive where your music files are. WMP will consider this part of its music library and will constantly monitor the NAS folder for changes. When you rip a music CD on your machine, it will show up in the other person's music WMP library a few minutes later, and that person can then sync the new music to his or her portable player.
Now let's replace the two PCs with Macs. First you'll notice they have trouble detecting the NAS drive, it doesn't show up in Finder. In order for network discovery to work, you will have to disable Leopard's firewall entirely, or mount the drive with a home made script. So you disable the firewall (feels really secure, doesn't it?), and voilá, the NAS drive pops up in Finder's left-hand pane. But you have to log in manually to the NAS drive, or again, write a script that does it for you. Or you can drag an alias to the Start Objects under your user account, then it will map to the NAS drive automatically on startup. Unfortunately it will also open a Finder window on every startup, but whatever. Right, now onto making the music files part of the iTunes libary. You'll find that iTunes can't monitor folders at all, you have to add files or folders manually. So every time you rip a CD on one computer, you have to go to the other computer, fire up iTunes and add the new files manually. You could of course share the library from one computer, but then the other computer can't copy those files to the portable mp3 player because the shared library is off limits to iPods. And eventually you'll discover that iTunes doesn't really like having its library on a NAS drive; sometimes it will default back to your local (empty) music folder when you update iTunes. Sometimes it will say the files don't exist and mark them with exclamation points, even though the NAS drive is clearly online because you're browsing it in a Finder window. It all feels so... whatever the opposite of modern is.