They have cogs on the underside to allow a better fit around the pulley and increased air circulation. The air circulation keeps them cooler, so they will last ionger. When you inspect your belts, look for cracks in the rubber, fiayed edges, missing cogs - anything to suggest it's getting brittle or worn. Replacing a belt when you're having an oil change is easy. Doing it by night at the side of the road is not.
Hoses are equally important.
Coolant is carried from the bottom ofthe radiator to the engine block, circulates through a waterjacket, and then returns to the radiator via the upper hose. A thermostat in the upper hose regulates the flow. Inspect the hoses every time you have the hood up. Run your fingers along the hose to feel for cracking. Squeeze the hoses to make sure they remain firm - a mushy spot is likely to give out at an inconvenient moment.