Simple:
- Efficient user interface. Do with 1 click things that take 5 clicks in Windows, like ejecting a Flash memory key.
- Better software. Better management of movies, digital photos, and so on.
- Lots of high-end software exclusive to the Mac (Logic, Final Cut, Motion).
- Stability to run multiple high end applications continually, without need to reboot, ever.
- Not a single virus issue on Macintosh for over 10 years.
- No need to maintain the computer's software. Forget adware, spyware, disk fragmentation, vulnerability to hackers, mismatched DLLs, or hunting down drivers for your printer or CD drive.
- Better build quality.
- One supplier, one warranty.
- All components and accessories (digital cameras, printers, anything) work natively, without ever needing to load a driver.
- A software update process that actually works.
- A system that allows a crashed application (and it can happen, especially with beta stuff) to be closed without causing any disruption to other apps.
- Lots of features and software "out-of-the-box" that are expensive and poorly written extras or shareware addons for Windows, such as FTP/Web servers, Java, development tools, compilers & programming environments, and so on.
- BlueTooth support that works consistently well.
- iPhoto. A great way to handle all your digital photos effectively, regardless of what camera you're using and so on. If you buy an Olympus camera for instance and plug it into a PC, you have to load up Olympus software. If you later change to a different brand, then those thousands of photos are in the wrong program! If your camera turns out not to be supported in Longhorn for 6 months after its release, do you think anyone will be able to help you?
What sums it up best is that since I've had a Mac, I've always been able to do the latest and greatest things and never have to worry about whether this printer or that camera is supported. When Tiger comes out, I can confidently install it and not have to worry about whether my Wacom tablet or my SonyErriccsson phone will work: they WILL.
When Longhorn comes out two years after Tiger, minus a lot of the features they'd promised (they've already scrapped WinFS, their own answer to Spotlight), can any PC user honestly tell me that it'll install flawlessly and all of their hardware and software will continue to work flawlessly? Or will all those people who rush out to buy Longhorn be telling me "Wow! Longhorn is GREAT ... but my mobile phone no longer transfers contacts with Outlook, but the new drivers are just around the corner!"
Finally, I'd have to rate Apple's attention to detail as being without parallel. On the first release of 10.2, the address format for Australian addresses in Address Book had the postcode incorrectly placed before the town/suburb. A week later, the first update was released and this was one of the several hundred minor fixes. I've never seen a serious problem with Apple software, only a handful of minor quirks like that, all of which are corrected very promptly.