Not quite sure where the claim is made by GM to change at 0% as my manual says to change it when the "Change oil soon" message comes up in the DIC in the C6. They also state that it should be changed once a years as a minimum. My guess is that GM considered the "kind of car it is" when they printed the manual and provided the oil life percentage monitor.
On the C5 the oil change interval changed as the series got older but as I recall it was at 7,500 miles in 1998 and as high as 14,000 on the 2004. The manual in one of the C5s said to change at 40% IIRC. With that in mind GM may have set the "Change oil soon" message at "0%" and changed it to read that way on the next year for the C6. One thing for sure is they have extended the oil change interval greatly in the last 8 or 9 years.
I've not seen the message come up yet as I change it at or near 10,000 or near
65%. At present I have 8,600 miles showing on the last oil change and a 78% reading on the monitor. Even that change interval depends on whether it has been driven hard or in dusty conditions. The only thing that would indicate that it needed to be changed in 5,000 mile is if it took a year to put that many miles on it indicating many short trips or lots of time parked.