They aren’t all designed to connect to your cold water line. In fact, most seem to specifically instruct you to connect to your hot water intake. You are right that most in the US have water heaters, but that doesn’t mean that the machine’s cycles will heat the water effectively for the full duration of the wash.
Maytag, Whirlpool, GE, and LG all recommend you connect to hotwater. Bosch (EDIT: Spelled this like the drug company not the appliance company) recommends cold. Depending on your machines cycles as well, the heating element may not get the water hot enough to make effective use of the pre-wash cycle. If your machine is connected to the hot water line and you purge the cold water from the line, you will see a more effective pre-wash (and thus more effective wash) than if you let it run cold.
They aren’t all designed to connect to your cold water line. In fact, most seem to specifically instruct you to connect to your hot water intake. You are right that most in the US have water heaters, but that doesn’t mean that the machine’s cycles will heat the water effectively for the full duration of the wash.
Maytag, Whirlpool, GE, and LG all recommend you connect to hotwater. Bosch (EDIT: Spelled this like the drug company not the appliance company) recommends cold. Depending on your machines cycles as well, the heating element may not get the water hot enough to make effective use of the pre-wash cycle. If your machine is connected to the hot water line and you purge the cold water from the line, you will see a more effective pre-wash (and thus more effective wash) than if you let it run cold.