In Belgium the only cable ISP has caps. 100GB for the cheapest plan (30/2.5), between 150GB and 750GB for the second offering (60/4) and between 250GB and 1250GB for the fastest (120/5). Those caps for the upper two plans shift dynamically depending on what time of day and what days you use the internet.
as far as I know no cable based ISP's have a cap, I think there are rumors that some might have one that's like 250-500gb a month, but I still have never really heard of anyone getting extra fees for going over it. As far as cell providers that have caps, then yes, that does make more sense as congestion can be an issue, but not as much as they like to claim sometimes.