Can't wait to have a go at it. It will probably be something like the tunnels in the first one. That was realistically the only way to get it, you couldn't even come close if you were playing the cases. There will also be more zombies on screen this time around.
There's no way you'll be able to kill 72k zombies just over the course of regular gameplay. It'll have to be similar to the first game.
Also you gotta remember that there will be way more zombies onscreen than in the previous game. Combined with the fact that the maintenance tunnels (or the FC equivalent) will be returning, I'm sure it'll be easy to rack up 72k in one playthrough.
Currently Playing Dead Rising (360) Currently Awaiting Dead Rising 2: Case 0 (360)
I would hate it if the harder/higher up achievements were just given to you by playing through the game in a normal way. They become less of achievements (with unlockable rewards) and more of just something to say you are playing it the right way.