That's EASY.... They do not have a cap on their data. Just because they are throttled doesn't mean they do not have unlimited data. Said it before and will say it again. Anyone who has unlimited data should get what they paid for when they bought that plan. Unlimited data at 2G speeds, not 3G, or 4G, or LTE.
People expect unlimited data on an AT&T network that in some areas can have speeds in excess of 40Gb/s when you signed up for a plan that was around 700kbs at the time?
And they are the people who call companies like AT&T greedy. LOL, you have to be kidding me.
Actually, I signed up for my unlimited plan when I bought the 3GS, on which I received 3G speeds.