This is true for AC and DC. Similar to DC in a car. A car battery can provide hundreds of amps. A fuse block is used for separating the wires from different components. While wiring that can handle hundreds of Amps could be used, it is cheaper to use smaller wire. A component rarely requires more than a few Amps of power to function so there is no need to use higher-current wire. The starter is the second issue. This is the main reason for high-current batteries in cars.