Are there any contemporary, major software programs that run only on the Mac, not on the PC platform?
If so, are they so freakin’ good that it would justify buying a Mac for that reason alone?
Final Cut Pro is supposedly the bees knees of video editors, available on Macs only.
There are very good editing applications on PCs of similar sophistication, but the consensus tends to be that FCP packs more bang for its buck.
I am not a Mac user, however.
The digital audio workstation software Logic Pro is held in high regard and probably sold some Macs when Windows support was dropped.
But it’s not like there aren’t great audio tools for Windows and Linux platforms.
I’m also sure there’s a significant amout of people who’d list the video editing software Final Cut Pro as their sole reason for buying a Mac.
But let’s say your main interest is computer gaming. Then there is no way anything in this sad list would get you to buy a Mac.
So, depending on the person, yes and no. There was no single program that made me buy my first Mac and there still isn’t one that alone keeps me on the platform. Ain’t competition great?
I’ve got a couple friends who are professional photographers, and they both swear by and adore Aperture.
There are PC-based apps for processing and cataloging mass quantities of RAW-format photos (They’ll shoot 1000 pictures on a typical day) but Aperture just works better for them. Part of why they come home with so many photos is that they usualy “autobracket” their shots - they press the shutter and the camera rapidly goes “pop pop pop” instead of just one click - one exposure is at the “right” values and the others are over and under. When they pour it all into Aperture, the software looks at all these trios of images and picks what it thinks is the best and hides the others. If the humans disagree, it’s mindless to swap them around. That’s just one of the automated “workflow” processes that Aperture does for them.
Yep, I was going to chime in with Aperture. However, Adobe Lightroom is available for both Mac and PC, does pretty much the same thing (I’d say more. I’d also say at its current state, it’s better).
Probably not what the OP is looking for, but the obvious example of a program available only for Mac is the OS itself, which is good enough that it’s the primary reason I use a Mac instead of a PC. Others may and probably will disagree, of course.
Chronos, I’ll venture to say you aren’t interested in the OS (which is just BSD Unix now for all intents and purposes) as much as the tight integration between the OS and the hardware possible because Apple knows precisely what hardware it needs drivers to support, because Apple is a hardware company that happens to sell software.
That is one reason Apple can sell Macs even though there is so little you can only get on a Mac. Stop trying to make Apple compete with Microsoft, for god’s sake!
For most users, the “OS” itself isn’t of interest. It’s the UI that is. That is where the Macintosh shows it’s superiority to Windows. The fact that the underlying OS is also superior is just icing on the cake.
And, of course, the other Apple-created software. I have no interest in iLife or iWork or things like that but it’s out there.
More precisely, I’m interested in the combination of the OS and the graphical shell bundled with it. But the fact that the OS is, at the underlying level, Unix, is in fact important to me for a variety of reasons, and I interact with the computer through a terminal window nearly as often as through the GUI.
As this thread has shown, most of the programs that run only on Apple are… made by Apple. And that’s fine. iPhoto is about as good a management tool for point-and-shoot digital camera users like me. That said, it’s the only product in the iLife suite I use with any regularity. Though the new iMovie might have some promise.
There’s also a metric ton of Mac-only programs made by independent Apple developers, but most of these are pretty small and relatively unknown by people who don’t already own Macs. Therefore, they’re unlikely to become the reason anyone buys a Mac. But anyone who does own a Mac knows that Adium is the best damn IM client ever created. 
Well aside from Adium, there’s Schoolhouse which I as a student find invaluable for organising myself and Journler which I use for note taking although that’s not its intended purpose. I know of no Windows equivalents.
Those could probably be replaced with Microsoft OneNote.
And my point was that you can get Unix, and specifically BSD Unix, much cheaper than you can buy a Mac. What buying OpenBSD and putting it on a Dell does not get you, however, is the tight hardware integration I mentioned above. Maybe the integration isn’t important to you. But if that’s the case, I humbly submit you are paying way too much for hardware and software.