I don't get the first point about zombies respawning. Do they just respawn out of thin air a couple of feet from you or do they come from off camera? Zombies respawned in the 360 version also, but with so many spread out over an area, they could always repsawn from farther away so they were never detected on camera.
Basically what I'm asking is, if you have your collection of a "dozen or so" zombies on screen and you start walking backwards through the mall, keeping them in your sights the entire time, are you going to be free from attack?