It's possible that they bought an indefinite right for this generation, but it wouldn't surprise me if the negotiated term was shorter, say 6 months. That limited term would to a degree benefit Verizon in that they would be able to lessen their investments into the agreement with the knowledge that before its expiration they would have a new crop of challengers to promote (next generation Samsung); likewise, it would benefit Google in that they would have had a large burst of 'only at Verizon' advertising at the products' launch (which level of focused advertising would have been difficult to get from any of the carriers if it had been available from all), and, at the termination of exclusivity, opening it with other carriers could help boost up sales through the other carriers (for those customers who didn't go through Play,etc) and ramp up awareness in advance of the next generation.