My new house (well, 3 years old now) has the same issues.
The garage floor had a crack all the way across before we even closed on it.
We replaced carpeting in the main room with tile two years later, and the floor all under was cracked.
Basically, the way companies are allowed to pour concrete is the cause. They used to require steel reinforcement (rebarb) and controlled curing temperatures. Now it's just dig, pour and go. Basically, cheap manufacturing and illegal alien laborers.
What will happen in your basement is if the water tables rise or if heavy rain hits, you will get water in the basement.