yes the cap can effect millions (assuming virgin media has that many customers, i dont know), but, how many of them actully reach that cap and have their bandwidth reduced? the bandwidth restrictions wont kick in for the average user because the average home user wont download enough that will trigger the bandwidth reductions, as for the people who do download so much that they get their speed reduced, well you downloaded lots, wtf do you expect to happen? as you said, virgin media could have kicked every single person who is a heavy downloader (a heavy downloader being someone who downloads so much during prime time that the cap would effect them), but then instead of whining and crying about the cap being in place, you would whine and cry about being kicked from virgin medias service.
If its a choice between there being a bandwidth cap that stops ppl who download lots during primetime, but doesnt effect other people, OR having high bandwidth users continue using high bandwidth, even during primetime, thus effecting other people who may only use the internet to view websites, or youtube or whatever. I would choose the bandwidth cap.
In the end the choice always remains, if you dont like the bandwidth cap, do your downloading out of prime time, dont download so much that you get capped, or simply leave virgin media. the choice is yours.