I believe this person is referring to a home without a basement. Probably a monolithic slab situation (heís probably out west). Therefore, the slab would, indeed, show in every room, since it is the floor.
Regardless, this is not normal, I believe, and should be investigated by the proper authorities, like Jay J said.
The cracks could pose an easy way for radon gas to enter the home, should that be a problem in the area where the home is being built. Minimally, they (the cracks) provide an easy access for crawling creatures and such. Should the cracks somehow be acceptable by all the proper authorities, I would, at least, want to have them filled in with a good silicone sealant before the carpet goes down.
Just donít wait too long before getting someone involved.