adamj: I guess I can give that a go. Is it not misleading then for consumers if my ISP is selling me a service 'as fast as my line will allow' when in fact what my line allows is being inhibited by the upload speed of the plan I have selected?

No, because UDP is not constrained by the upstream. If you try playing a high bitrate file in windowsmediaplayer off a proper streaming server (not http) then it will easily stream 4 megabits which looks very very good. That will coexist with you browsing the net since its not reliant on upstream much.