The crucial point investors (and smart generalists) must understand is that Pandora doesn't have to be as big as Apple. It never will be, nor should it strive to be. On the flip side, Apple doesn't need to, should not and likely will not spend time striving for dominance in areas where Pandora already has dominance or has achieved scale or continues to build out to scale.
There's likely a dedicated team of talented people working on iTunes Radio (though, their gatekeepers refuse to even respond to my requests to converse with them), but it's not Apple's bread and butter. It's a means to the ends of, primarily, selling more hardware and, to a lesser, but somewhat important, extent, ramping up a fledgling mobile advertising business.
That's not to say Pandora stock hasn't run a bit too far. After I watched it triple from the $7 range I was bullish in, I couldn't do anything but throw cold water on the rally. But all of this is to say, iTunes Radio will do well. It, along with, but not without Pandora, will be one of the survivors doing pure-play personalized radio. The services will remain distinct enough, not only in user experience, but in how the respective companies leverage them to make money.