And depending on the limitation, i would classify it as predatory behavior. For example, there are few ISP which advertise their internet with claim unlimited usage but also do one of these,
1. Very strict data caps/FUP[1] before your speed is slowed down significantly. In my country, i've seen few ISP which offer 50 Mbps with only 300GB monthly FUP. Even comcast (one of ISP in USA) has 1.2TB limit and then offer actual unlimited plan[2].
1.2 terabyte is alot for a single day. a DVD-R disc is about 5GB right? that's like downloading over 200 DVD movies or something in a single day. i'd say 99% of people don't have that type of need. shouldn't have that type of need and if they do then they're on the wrong plan. but if they do offer a truely unlimited plan as you say then that's what that is for i guess.
2. Threaten to terminate their service for customer who use lots of data[3].
Homeboy downloaded about 18TB of data in one month and wonders why they threatened to cut him off. One mnth. 18 terabytes. you do the math. equals other people can't use their internet service because homeboy is downloading Linux ISO images like crazy. probably trying to sell them.
3. Attempt to throttle VPN and Torrent[5] connection.
personal internet service is not really meant to do things like share torrents. lets say Joe tries to run bittorrent 24/7, then people all over the globe are going to be hitting him up for pieces of files. so what just happened is all those people became non-paying customers of Joe's ISP. they don't like that.
unlimited is only unlimited to the extent that you don't cause a problem with other paying customers or the ISP thinks you might be. then you're not on unlimited anymore.