They didn't pay for a "unlimited full speed 15gb then after that 32kbps" plan, they paid for an "unlimited plan."

I have the same "unlimited plan," and the terms of the plan have nothing to do with data limits. There is no "you get this speed for X GB then after that get slowed down" - you are guaranteed the fastest speed available except in cases where the tower is throttled. They sell the plan by saying "you most likely won't ever experience a problem unless you go to a baseball stadium with 20,000 people on their phone at the same time."

What Verizon did is throttle their account, not a specific tower and not the users of only that tower. They throttled their unlimited account, which did not have terms like you suggest.