They look hot on the C5 because its a photoshop job, and the wheels were incorrectly "sized", as they appear more like how 19/20s fit a lowered C5.
The rest of the pics were of a C6 which is a narrower (body) than the C5 is (gee, maybe also why they changed C6 offset to be tucked in more?). So, the widebody 19x12s will definitely stick out of base C6 fender more than they will mounted on a C5. Not a valid comparison.
I'll let Steve further guide you with specific fitment and offset questions, since he knows it all, but be sure to keep in mind which day of the week you ask him...
The wheel that sticks out on Tues may very well need a spacer on Wed.