Does anyone know the main differences between the Kenwood 5100, 7100 and 8100 units?

Crutchfield listing of differences between 5120, 7120 and 8120

pat----

Crutchfield doesn't give much help between the 7120 and the 8120. All it says is built-in bluetooth. I was reading around and someone was saying the 7120 doesn't support the new generation ipod video's? Is this correct? Are they talking about the ipod touch, or ipod classic? If anyone has a 7120 and can watch video's from their ipod classic that would be good to know.