There's always a moment of uncertainty before you get your hands on a music game. That tough-to-pin-down feeling of connection to the music - something that the Guitar Hero series has always nailed - can't be spotted in screenshots or even identified during a video. It's not until you get your paws on the peripheral that you can truly make a judgement.
DJ Hero has a bigger hill to climb with newcomers than its rock-based brethren as well. Everyone knows the basic functionality of a six-string, and can do a decent air guitar impression, whereas the purpose of a cross fader remains a mystery to most people.