Odds are that you will probably get a couple of punctures in 4 years; if you do, your tires are paid for. If you damage your rim in the process, they are paid for too. The PS2s are over $350 a piece and the 19" factory forged wheels are a pretty penny.
Also, the warranty covers any tire/wheel that you have on your car at the time of the puncture/damage. If you decide to change out the wheels, they are covered as well (not sure what the limits are but factory wheels are not cheap).