yes, but those people that live up north close to canada don't have to worry about very hot climates and so would choose an oil that is suitable for very cold conditions and moderate temps.
People living in hotter average climates will choose a slightly thicker oil to match the average temps.
You can't expect people to change oil depending on what season it is, you just chose something that suits the average tempreture and driving style of where they live- you don't have to be exact with the viscosity, as long as the oil is good quality, changed regularly and is 'about right' with the viscosity, its good enough.