It's simple really, there was a $100 discount in the midwest for upgrading to a 4g phone. For whatever reason it was only valid for those customers, maybe they saw that their 4g sales were sagging in the midwest so they used that promo as a way to move more customers to 4g.
All other discounts are if you have upgrade discounts for renewing contracts, some still have their new every 2 discount because they haven't used it since Verizon canceled that promo, other's don't.
I've always felt like arguing for something that doesn't apply to you is a bit childish, you should play by the same rules the rest of us have and pay what we've paid. Complaining to get your way only hurts the potential of them doing discounts again because they'll see that it was abused last time, so they'll just not do it the next time and save themselves the headaches.