To their surprise, AT&T began sending out notices to them as well, threatening to throttle their download speeds after they passed the mere 2GB download mark. Considering that people on tiered plans of the same price get 3GB, that seemed unfair.
AT&T has now chimed in on the whole drama, saying that according to its calculations, the top 5% of data hogs consume at least 2GB a month on average, hence this arbitrary cutoff consumption for some. The carrier also said throttling is decided on a case-by-case basis, depending on the network strain and consumption patterns.
It also mentioned that less than 1% of smartphone users have been throttled this way. Not that it's any consolation if you are one of them, or that this makes it fair, but that's AT&T's official take on the matter. The catch here seems to be that the 2GB minimum consumption of the top users AT&T uses as an argument, seems to be statistic from last summer, and things might have changed significantly since then.