Bandwidth is insanely cheap compared to last-mile infrastructure. Bandwidth caps are basically just a way to soak the customers who use the service more and are, hence, willing to pay more.
Well if you have a lot of contention in your last-mile infrastructure bandwidth caps make sense. This applies to shared infrastructure like a coax cable network, or the connection up to a DSLAM.
Yeah, there's no contention AT ALL up to the DSLAM. DSLAM is DSL Access Module. Every DSL customer has their own dedicated copper pair from the DSLAM to their house--- it's their phone line. There may be congestion between the Central Office where the DSLAM lives and the rest of the internet, but in practice that rarely happens. The big limit on DSL is getting reasonable speeds a mile down the line over ancient copper pairs that were never intended for the purpose. Don't people remember the old Cable vs. DSL commercials, where the DSL companies were showing cable customers furiously calling each other bandwidth hogs and telling them "log off!"
