How much trouble does winter weather cause for folks in Detroit who do not have cars? How close to downtown Detroit do you need to be to still have an acceptable amount of freedom of movement without needing a car?

From personal experience living in Denver (we get roughly the same snowfall as Detroit). I found driving in the snow much more annoying then walking/taking the bus.

I'm guessing Detroit's lack of car ownership is partly due to income.

Property has stayed relatively cheap around here. So people working service jobs can afford to live closer to work sometimes. But I think the answer is a combination of unemployment, inability to afford a car and people driving without license and registration which is used for this data explains it more than a functioning public transportation system.