I have seen lots of large live oaks (1 to 3 feet diameter) next to slab foundations, and many were there when the house was built. Apparent foundation damage from these trees is rare; roof and fascia damage is another story. Anyway, I have heard it said that the tree is looking for moisture and nourishment and there is very little of either under the slab. Therefore the tree roots don't grow under the slab foundation and no damage results. I'm not an arborist, but it makes sense to me. Another consideration is that the tree sucks a tremendous amount of moisture from the soil daily. If the tree is removed soil moisture conditions are dramically altered, and in Central Texas expansive clay soils, that can result in heaving clay soils that will damage a slab foundation. In my reports, I always commented on the tree and the possibility of damage to the house (roof and fascia), but I never recommended removing the tree. If the buyer was concerned, I'd pass the buck to a structural engineer and an arborist and let them fight it out. The arborist always said save the tree; the engineer would worry about future damage, but was usually hesitant to recommend changes because nobody knew what the result might be. Around here a large oak on the lot, even next to the house, is worth thousands in appraised valve.