If they retained the 3rd gen rear brake disc type, and I think they did, the e-brake engages a drum-style brake that acts on the inside portion of the rear disc.
In any case after 130,000+ miles on mine they still grab just fine on the OE e-brake pads. I would guess the cable needs adjusting...I think that can be done up on the handle end of it...Correct me if I am wrong by all means.
Edit: if you look at the spring in the pic between the pads there is also a sprocket like wheel that can be turned to adjust. The rear discs have holes in them (covered by rubber plugs) so you can turn the rotor (wheel off) to line it up to be able to adjust. I am not sure though where it is recommended the adjustment be made (at the handle end or the rotor end).
Sent possibly from the shitter on my HTC EVO, bizneeaatch...