That always bothered me. Romero wanted this to be taken seriously, but the concept itself doesn't make sense. Cash would be worthless if the banks and government weren't there to back it up. The scavengers have access to banks, cash drawers, jewelry stores, museums, etc... If that's all it takes, they could loot themselves a good-sized fortune pretty quickly. What did the rich people who fled to the gated community have when they arrived that would buy better living conditions? Credit cards and check books? Useless after society collapses. Cash? A lot of wealthy people don't carry it. The guys who go out and supply the goods should have the bargaining power.

Zombies becoming more intelligent over time doesn't make sense either when you consider their brains would be rotting along with the rest of them.