You can pick who you want to blame for this "failure to charge".
You could pick Apple...
Apple switched the interface for the newer iPods from firewire to USB. There are just more consumers out there with usb equipment (windoze computers) than firewire equipment (Macs). Go to the Apple iTunes forums and read the howls of rage from consumers who have purchased many iPod music systems that no longer charge their newer iPods.
You could pick Nissan...
Here is the cube, and new vehicle introduced well after Apple switched to a usb charger. And what interface does Nissan install? Of course, the firewire cable. Reason, well they just might have purchased a few containers and have a few left in inventory so install and use up the inventory. The number of the older style firewire units is much greater than the newer usb interface, so the chances of having this charging problem become a major launch problem for Nissan is reduced -- for now. Watch for the next model year to have been upgraded to the usb based interface.
Or, you could blame yourself...
Hate to say this, but "You were warned". In the brochure that came out with the introduction of the cube, there in the fine print is a tag saying "iPod charge through the Interface System may only be supported via use of Firewire devices. See dealer for details." My dealer did not even know that XM Satellite was included in the "Tech" package, so charging issue would have been an unknown as well. In fairness, I bought the cube the day it arrived (mine was the first registered for the road here in Ontario) so it was all very new for everyone.
So, enjoy your cube and tunes. And if you really need to charge, then go out and purchase a firewire to usb charge adaptor. Nissan nor Apple will buy one for you.