Say what? Every ISP charges more for higher bandwidth (e.g. $X/mo for a 5Mbps connection, $X+Y/mo for a 20Mbps connection, etc).
If (for example) Netflix starts serving up high-definition video, the people with slower connections will have lots of pauses and stutters because they didn't buy enough bandwidth, and thus will be motivated to upgrade their connections (and pay the ISP more money) or do without (and reduce the ISP's bandwidth needs). If customers already purchased connections with enough bandwidth to watch high-definition video and the ISP can't handle the load... well, it sucks to be them, just as it sucked to be Max Bialystock when the house of cards fell down on him.
Good point. I think I am confusing bandwidth with total usage. The ISP will sell you all the band width you want but they have practical if unstated limits on how much you can utilize that bandwidth to the max. It is particularly acute on the wireless providers but even the cable providers cannot give everyone maximum bandwidth all the time. Try getting a high bandwidth then utilize it to the max. On most cable ISPs a few people can get away with but if too many try it everything slows down.