Garage and Basement slabs take a lot of abuse. They have to support heavy cars and trucks and resist ice, dirt, salty water, de-icers, gasoline, motor oil, antifreeze, and other contaminants. Plus, since few garages are heated, they have to tolerate freeze/thaw conditions. But a garage slab that has been carefully planned, installed, and cured should have no trouble providing years of crack-free performance in any climate, even under the toughest conditions.
The floor is the last portion of the basement you will pour, after completing the footings and the concrete walls. Usually poured in sections, the basement floor must be level and care taken to prevent future cracking. Unlike pouring an open slab of concrete, the basement floor has the unique aspect of sitting within vertical concrete walls so some special techniques will allow you to smooth the concrete from only one side.