I had to google this. According to ehow, slab is straight up welfare. It's like building your house on top of a parking lot. No basement. It also drives up the cost of fixing anything under the house, so that means things are less likely to be fixed. A shitty house with broken plumbing stays broken forever. Slab is also low to the ground because concrete is expensive. Crawl space is better. Things are easier to fix and therefore more likely to be fixed. They're also higher above grade; more resistant against water damage and floods.
Then again both of those would be considered welfare around here. We have basements here. The house doesn't need to be xbox huge because it has a whole extra floor under the main level. I live in the basement of a house right now. Rent's the same as an apartment but it's bigger, less shitty, cost less, and my only neighbor is the home owner upstairs instead of meth heads typically found in apartment buildings.