Not everywhere. I always thought data caps were mostly in place in areas with ISP monopoly, but I'm moving to an area where Comcast is the only viable option, and they don't have any cap.
Maybe it's in populated areas where the infrastructure is not that great. It's hard to really grasp the logic since they claim that 98% of their customers never hit the cap. So what's the point?
To keep someone from reselling their bandwidth for commercial purposes. Like running lots of servers or starting up a wireless Internet provider and using the residential connection as back-haul/peering.
Maybe it's in populated areas where the infrastructure is not that great. It's hard to really grasp the logic since they claim that 98% of their customers never hit the cap. So what's the point?