From the Line 6 website:
FREE HD AMP MODELS AND MORE FOR ALL POD® HD PROCESSORS
Power-boost your POD HD multi-effect with an additional six HD amp models and five amp parameters – all for free! Why? Because we want to thank you for making POD HD multi-effects so successful!
Firmware update v1.3 includes six HD amp models based on* channels from three classic American combos (the “Vibrato” channel of a Fender® Deluxe Reverb®, the “Vibrato” channel of a Fender® Twin Reverb® and the “Bright” channel of a Fender® Bassman®), two British half stacks (the “Normal” channel of a Park 75 and the “Normal” channel of a Marshall® JTM-45 MkII) and a high-gain Line 6 original.