Cars, like sedans, with slanted rear windows never seem to have windshield wipers on them. On the other hand cars, like mini-vans, with vertical rear windows generally do have windshield wipers on them. Yet it seems to me that the vertical rear windows would need them less than the slanted windows. Is my intuition about vertical windows needing them less incorrect?
In order to see through a wet window you need to have a uniform surface: no big drops of water on it.
Cars, like sedans, with slanted rear windows might not need wipers since air already wipes water from the window. In case of vertical rear windows air is deflected from the abrupt read ending and so it doesn't flow fast on the vertical surface. Then it doesn't wipe water.