All valid points and yeah it makes for good TV but it's not that realistic IMO... If you can picture a zombie apocalypse being realistic!
You would think at some point questions like this would pop up...
-Are we absolutely sure there's no real government anywhere? Our group has only covered a relatively small area of geography.
-If we head to a colder climate will the undead freeze or at least be rendered far less mobile?
-If we head to a more mountainous area will it (like the cold) make it more difficult for the undead to traverse the area?
Also at some point the bodies would simply degrade to the point of becoming immobile. In the graphic novel there are references to this, i.e. our survivors noting the physical changes of the zombies and their continued degradation. So far we haven't had any of that in the TV show.