The tires do save fuel to some extent by using special rubber compounds tuned for less rolling resistance. Generally the tradeoff is between comfort, fuel efficiency, performance (and of course cost). These tires sacrifice some ride comfort and grip for low rolling resistance, but the special materials make the sacrifice less significant.
http://en.wikipedia.org/wiki/Low-rol...sistance_tires
Note that rolling resistance is the reason why underinflated tires give less fuel economy - they're harder to roll down the road than properly (or over-) inflated tires. However for safety and tire durability do NOT overinflate your normal tires to save fuel!