Down here in GA... CO water lines from the street to houses rot after 20-30 years... and no... it is not from the inside out. Folks NEVER replace with CO anymore... always with PVC or some miracle pipe.
BTW: WHO warrants the loop? The warranty is only as good as the co offering it. As I understand it... WF is the one that warrants the loop... (please correct me if I am wrong). Gotta remember: A local contractor may not be there next year... or when he retires... or when his son takes over and chooses to change the name and not honor previous warranties.
IMO: one should always be wary of warranties... rather use old fashioned common sense about them.
The system mfr. If you know what you're doing it isn't a provlem