It simple really Slacker isn't interested in creating docks or hardware period. I think they will continue to do an exclusive agreement with RIM for the Blackberry to cache stations. Once this exclusivity is over who knows maybe by then Apple will get over themselves and allow at least a few stations to be cached to the iPhone or iPod Touch's memory.
I don't see a device like this selling for Slacker!
Yeah, but it would be an accessory more than it would be hardware. (I know, pushing it slightly). And if done right it wouldn't cost a lot to manufacture. They could have someone like Belkin or Griffin make it, since they already do iPhone accessories anyway. Like I said, Random Thought.