The iPod is doomed. Not this month, not this year, and maybe not the next. But soon enough, Apple will lose its hold on the marketplace for both digital-audio players and digital songs. It's inevitable. Already the iPod's features are being copied by Samsung, Dell, iRiver, Sony, and others. Competitors are adding tuners, cameras, gaming, and more to devices. They're rolling out a host of new music services. Meanwhile, the iPod has not changed much since its debut four years ago -- and Apple's latest iteration, the iPod shuffle, has met with limited success. The competitors will win. Why? Because...