Too simplistic by half
I have virgin media 20MB, it used to be shite, then it improved, I regularly get 7MB downloads now. No where near the 20MB, when I complained Virgin insisted on running speed tests with the PC in safe mode, because according to them the PC overheads effect the download speed. They were right it did speed up by around 10 - 20%. You also have to take into account the server speeds you are connecting to. In the main I seem to have a DNS Lookup Problem but who knows if this is Virgin or further down the pipe.
All in all a crappy industry which makes claims they cannot match and in some instances are out of their control. Any other industry and they would be straight into court.
Man stealing my wallet because that is what the ISP industry is doing.