It's not the tools that make the artist. In my opinion the reason why we see a lot more mediocre or worse pages coming from PC users is that there generally is more PC users than Mac users as in, everyone and their grandma.
Simply having or using a Mac on a daily basis doesn't make you a better artist. The College I'm going to school to to get my graphic design degree has a lot of Mac's but I find that the difficulty level on using Photoshop or such programs isn't any more or less than using them on the PC.
I have seen quite a bit of bad artwork coming from Mac users as well as good work. It's kind of like handing someone a better pencil, it doesn't automatically make them a better artist but it sure doesn't hurt. Sometimes though it is sort of just a waste of money to spend so much money on a tool if the person isn't serious about what they want to do with it.
It has been my opinion that it shouldn't matter what you are using as long as the end results are of the highest quality that you can put into them. So picking either a Mac or PC should boil down to what you prefer in your user experience rather than thinking that having either will magically make you the uber-artist.
It is however good to try out several different platforms because you never know if you might like one over another. I myself have tried many. I'll plan on sometime owning a Mac, because face it.. it's too tempting not to. But I will be keeping a PC around at least for the games I have which have no Mac versions.