It's a lot different in the UK, with ISPs getting bent over at £1.2M a year for a 622Mbps Central from BT to them, and most of the traffic shaping aimed at giving a reasonable service to the majority while preventing the majority saturating everything with Dodgy.Goat.Pr0n.torrent.
Centrals don't apply to the LLU providers and NTL/Telewest, but it's the same idea - limited expensive resource, more than enough users to max it out.
Similar standpoint applies to prioritising an ISPs own usenet/FTP/stuff, if they're hosted locally they aren't paying for transit.
Nowt stopping you migrating either, versus big chunks only serviced (chortle) by one provider in the US.