Headphone Amps are for people who are serious about listening to music with headphones. They give whatever device you're using to listen to music the extra power it needs to pump high-grade audio to super high-end headphones. Audiophiles find them to be absolutely necessary.
And now Audio Technica has gone and combined one with an iPod dock. Which on the one hand is good, as it combines two common gadgets, but on the other hand might not appeal to audiophiles who listen to lossless audio files. The iPod doesn't support FLAC, after all. But hey, if you've got $560, this bad boy can be yours.