Essentially it's OK to lie if you offer a product but not if you buy it.
It also highlights that operators try to tie specific devices to services instead of managing the "problem" on the server/provider side.
In all it's about being open, not locking in the customer. It's better to be straight with the customer about the fact that there is a ceiling on the usage.
Then there's another question of how the users really are able to run up a traffic volume in the terabyte class. That's actually pretty amazing, but if someone is streaming HD movies I can imagine that it may be chewing away the bytes pretty fast, but according to some a HD movie is about 2GB/hour. So that means 1000 hours for 2TB - and that means that you need to watch movies every hour in a month and still not reach 2TB.