You have to be part of a program no one uses that Verizon has been trying to get more people to use to lock customers into their services. That's just another deal to try and get them in, Verizon is probably paying $100 themselves to give you that price.
It's not wide spread as most Series S are still $249-$299. That $150 is to attempt to increase more participation in the rewards program. In fact, they made it so if you are a new customer you're automatically enrolled.
I doubt they have many units for this program as most are still selling at normal price. Unless Verizion wants to lost a boatload of cash paying to reduce the Series S price.
These gaming outlets like Gamespot are doing more marketing for this deal than Verizon is likely a limited supply which explains the March 31st deadline, they probably aren't expecting many to rush for this deal, just a few new and existing customers that may use the program because of this deal.
It's still a pretty great price if you can get it. You can only get one though.