If a 20-30% downpayment seems completely unrealistic, then you are probably not in area that you can afford. A home is like a car, in that nobody forces you to buy the Porsche, and you can always buy something in a cheaper area. A location with a median home value of 600k is definitely in the "Porsche" category of locations. Go find yourself a Camry.
Never said it was unrealistic–just meant it wouldn't happen immediately. By the time I have it available (2-3 years), my credit score will be improved too.
Also, our rent is very low here ($2K for a 4bd home on 1/3 acre in a great neighborhood). We just happen to be in an area where buying vs. renting is out of balance.
And your car analogy breaks down real fast. There are many more factors which can/do prevent people from moving to other cities.
