said by JTY:
Most (all) implement UPNP, so they just open the needed ports on your home router.
I'm well aware of UPnP. I was countering Smith6612's assertion that game consoles complain if you're even behind one NAT. Obviously there are solutions to work with the issue in those millions of cases...and those solutions that work for the residential router also can (but not necessarily will) work for ISP NATing devices.