They are almost more useful, since a large part of the cooling season is below 80F but still has moderate humidity. IF you add enough insulation and have enough thermal mass, when the average daily temperature is below 65F, all you need is a dehumidifier and ventilation.

In the south, much of the cooling season you have enough sensible heat to use yoru AC to dehumidify. That's not the case in the north, but you still have the same indoor latent loads as well as air leaks.

Remember, most douthern climates are somewhat tropical. In the norht, you have a wide, wide range of environemnts. In South Dakota, it gets almost as hot and humid as most sourthern states for a few motnhs, but it also gets nearly as cold as parts of Alaska in the winter. The desing temrpatures in a few places there are about 110F apart.