PC may not be the only computer that exists, but it's almost certainly the most widely used. Just because Mac's in recent years have been getting moar games, doesn't necessarily mean that it'd be a good move to dev for them. At least, not solely. For a new developer.
In my thinkings, and I've actually heard this before from several people, PC is the smartest platform for a small game dev to use, since it's used worldwide, relatively cheap to build with, and getting your game out there into the mainstream is that much easier.
Just my two scents. I very well could be wrong. I know the app market, both iOS and Android, is a pretty good place too. Arch or Deep would probably know more.