Infiniti has had the G35 in an AWD offering since it's introduction. Nissan more then likely will not off a Z in awd due to the conflict of interest.
Cars arent just magically appearing in AWD. They've been around forever throughout Ford and Chryslers line up, as well as other companies.
If you are shopping around you need to actually compare the AWD systems in the two vehciles. IMHO Infinitis "Atlessa" AWD system is good. It is not on par with Subaru's or Audi's. The platform is RWD bias and can/will transfer power on slip.