Because the iPhone and iPod touch measure max-device-width in logical pixels rather than physical pixels even with the Retina display (as they should), the original media query used for the iPhone should be enough:
@media only screen and (max-device-width: 480px) {
/* iPhone CSS rules here */
}
You’ll only need (-webkit-min-device-pixel-ratio: 2) if you need to target the Retina display separately.