What the builder should have done is drive over the landscape with a box blade to create a final drainage grade. If that wasn't done, you might be in trouble when it rains.

There has always been an alternative to core aerating. Landscapers never suggest it because anyone can do it and it only costs about $0.50. Golf courses are where the process is used most. It involves spraying the grass with a surfactant. The one used by golf courses is called Cascade. It's basically really good soap. You can get the same effect by spraying your yard with any clear shampoo at a rate of 3 ounces per 1,000 square feet. Spray, irrigate a full inch (as measured by cat food or tuna cans), and repeat the shampoo/irrigation in 2 weeks. This really does work. Of course it has been working on golf courses for years, but the homeowners never made the plunge to try it out. Cascade is very expensive. Shampoo is very cheap. But the transition has been made and now we're spreading the word. Everyone, and I mean everyone, who has tried it is impressed. I was very skeptical at first...and now I'm one of the chief evangelists. One treatment should last years. I did mine in 2011 and it still gets soft every time it rains or I water. Also you cannot overdo it. If you miscalculate and apply double, or triple, or or even 10x or 20x, it seems to work just fine. But 3 ounces per 1,000 is all you need.

The builder did do a final grade. There was just no topsoil added before the sod was laid.