I think I know the reason why Hyundai requires you to buy their iPod cable for models like the Genesis. The reason is that Hyundai didn't wanted to add in an authentication chip made by Apple. With said chip you could just use the iPod sync cable and it would work just fine with full integration. However, it only works on 5th gen iPod's and up. The Cable converts the iPod's USB to it's format and the unit tells the iPod what to do. I don't think Hyundai didn't want to limit compatibility and spend the extra on the authentication chip. I recommend you to buy the Hyundai cable if you want full iPod integration.
Edit: The Hyundai iPod cable also does the decoding of AAC files to the head unit. Protected or non protected.
Edit: The Hyundai iPod cable also does the decoding of AAC files to the head unit. Protected or non protected.