Apple is marketing to people who have a few characteristics.
1) Middle/Upper income folks who are willing to pay a bit more for a better user experience. paying 500 more for a computer is not a huge deal if you have a decent income.
2) People who like to have fun with technology. No other platform offers as many entry level tools (the whole iLife bunch and more). This includes people who like to shoot a lot of digital photos or video. It's the whole digital hub concept. People are starting to buy into it.
3) Music enthusiasts and fans ages 12-35.
4) Professionals in media and design.
The first two groups do overlap, but it's a huge market. Way bigger than 5% or whatever. Apple's problem is not really pricing. These are the same people who pay $500 to get seats that warm up your behind. Apple's problem is the status quo. People who should consider macs don't, because of a stigma of incompatibility that developed in the 90's.