But of course they wouldn't go to prison would they?
Probably not, but they could go through an awful lot of hassle unless, as you suggest, great care was taken to ensure that no such person was never accused in the first place.
Better still, would be if the rip-off merchants marketing vastly overpriced music, movies and software arranged for digital only 'rush release' copies of their wares to be legitimately available for, let's say 25p per MP3 and possibly 75p per movie, and maybe a whole £1 for a program. Obviously, these would be just the main product, no extras, no blu-ray, no printed manual, no case, etc, etc.
There is no financial impediment to doing this, it's only unrelenting greed that stops them. If prices were fair, people would buy rather than go for illegal copies. This theory is already proven beyond any doubt by both the Android Marketplace (now Google Play) and iOS App Store, with something like half a million apps between them, few of which are regularly pirated.