USA needs India as much as India needs USA. Each party has aprehensions over their past histories. India needs to keep a free hand in making her own policies and goals whilst keeping friendly relations with USA.
India needs strong technolgy, and American technolgy is probably the most advanced and is certainly tested. India could become an innovation partner in the relationship. A strong defence is needed to avoid a war, perceived weakness in the past has resulted in invasions. It is only in peace, that India can grow very fast. Plus, there are synergies in military technologies being transferred for civil industries.