Good question mate. Why do people say that "Macs are better than PCs with graphic design"? I'll tell you a few reasons why. Keep in mind I'm a jack of all trades: I do web development, graphic design, videography, etc. So I'm VERY knowledgeable about every bit of these professions. 
Anyway, since I've used Macs and PCs extensively in the past several years, doing all sorts of stuff, I'll say that Macs UI and environment are much more user-friendly than a PC. It's more efficient at certain tasks, and the UI in OS X helps to establish it.
Expose is one of them, as you have several windows opened up, and you really need to find that one window, but you'd need to go through a ton of them just to find it. Expose solves these problems pretty well, since you can either search by all windows opened, or by application. In Windows, you can either just try looking for it on the task bar, or use Alt + Tab to try and cycle through the dozens of files you have opened. Or...You could try and use Flip3D in Vista, which tries to be like Expose, only every window is stacked, which...makes it almost useless. Also, if you Apple + Tab (same as Alt + Tab in Windows), you can select an App, and get to your Apps windows, as opposed to just a single window in Windows. OS X is more elegant and efficient at these tasks.
Hot keys is another helpful perk that OS X helps with. With Windows, you have to use Alt, and type in a 4 numbers with the keypad to get a special character, which once you remember and get used to it, you'd be pretty efficient at it. But OS X takes it one step further, and by just using the option and/or command key, you use one key from the keyboard to get a special character. Again, once you remember the hot key, you'll be efficient. Since it only takes one step in OS X as opposed to four in Windows, OS X is more efficient for designers.
So let's move on to Fonts. Macs display fonts more accurately than Windows, period. I've never had a font issue with OS X. It's always with Windows that I've had issues with, even with a font manager. If you worked on one platform with say, a photoshop file or flash file, you'll notice that fonts that you lined up at a certain ruler point, that it's not accurately lined up in the other platform. If you're working at an office that has a mixture of PCs and Macs, I've found that this became very problematic. So, as the solution, we always came to the conclusion that Macs will be used for designing, be it for web, print, or motion graphics, etc. PCs were best with tasks such as programming, word processing, etc. If there is an office environment with just PCs, then it's best to just stick with that, and vice versa.
Critical designers have found that Macs are best with designing, as efficiency is always helpful.
Anyway, since I've used Macs and PCs extensively in the past several years, doing all sorts of stuff, I'll say that Macs UI and environment are much more user-friendly than a PC. It's more efficient at certain tasks, and the UI in OS X helps to establish it.
Expose is one of them, as you have several windows opened up, and you really need to find that one window, but you'd need to go through a ton of them just to find it. Expose solves these problems pretty well, since you can either search by all windows opened, or by application. In Windows, you can either just try looking for it on the task bar, or use Alt + Tab to try and cycle through the dozens of files you have opened. Or...You could try and use Flip3D in Vista, which tries to be like Expose, only every window is stacked, which...makes it almost useless.
Also, if you Apple + Tab (same as Alt + Tab in Windows), you can select an App, and get to your Apps windows, as opposed to just a single window in Windows. OS X is more elegant and efficient at these tasks. Hot keys is another helpful perk that OS X helps with. With Windows, you have to use Alt, and type in a 4 numbers with the keypad to get a special character, which once you remember and get used to it, you'd be pretty efficient at it. But OS X takes it one step further, and by just using the option and/or command key, you use one key from the keyboard to get a special character. Again, once you remember the hot key, you'll be efficient. Since it only takes one step in OS X as opposed to four in Windows, OS X is more efficient for designers.
So let's move on to Fonts. Macs display fonts more accurately than Windows, period. I've never had a font issue with OS X. It's always with Windows that I've had issues with, even with a font manager. If you worked on one platform with say, a photoshop file or flash file, you'll notice that fonts that you lined up at a certain ruler point, that it's not accurately lined up in the other platform. If you're working at an office that has a mixture of PCs and Macs, I've found that this became very problematic. So, as the solution, we always came to the conclusion that Macs will be used for designing, be it for web, print, or motion graphics, etc. PCs were best with tasks such as programming, word processing, etc. If there is an office environment with just PCs, then it's best to just stick with that, and vice versa.
Critical designers have found that Macs are best with designing, as efficiency is always helpful.