Now, T-Mobile may object to certain kinds of traffic (torrents, etc.) but that opens up a whole different can of worms. If the high-volume data consumers are actually causing a problem for other users, then T-Mobile probably should consider expanding their bandwidth with new equipment.
Trying to squirm away from the term "unlimited" because of a few inconvenient users with inconvenient bits, however, is just weaselly as hell and avoiding the real issue.