The platform for creating the graphics doesn't really matter. You can create the same things on Windows or Linux.
Macs tend to have a much stronger focus on design rather than functionality. If you look at the same application on a Mac or on Windows, you'll often find that the Mac applications are much prettier, and more responsive. This is particularly true for animations on a Mac - they are far nicer than on Windows. Same goes for animations on an iPad versus on Android - iPad animations are much nicer and smoother.
I find that everything take much longer to get done on a Mac, but during that time, you are really forced to pause a bit more. That slowing down sort of gives you time to stop and smell the flowers, if you'll permit me to bastardize that metaphor. So it kind of makes sense that if everything is tortuously slow to get done, it might as well be beautiful while you're doing it. Kind of like giving you a headache and then some morphine to deal with it.
But Photoshop or any capable image editor will let you do the exact same thing as the graphics you typically see on Mac sites. It's really more about the designer than about the platform. You'll also see the same kind of graphics on a lot of non-Mac sites. The Mac sites tend to be more consistent with some design elements that they use that are common in the Mac platform.