I think this cable appeals to people that just want to connect one cable to the player that charges and connects the audio and be on their way. Most people just connect a 3.5 cable and just run off the battery. With 30+ hours of audio playback, I think this really isn't that big of an issue.
It would be great if it also had a USB connector and if when connected the player switched to UMS mode, so that you can plug the player up to stereos that have a USB jack and then you can control the player from the head unit. Even if it just acted like a remote and didn't display any song information, you could at least set it to shuffle all and skip around.
Most iPod car stereo interfaces aren't really that great, and the people that get them have to live with their faults because there isn't anything else out there.