Many people jailbreak ipads and iphones because they don't want to pay for the more expensive apps. An example of this is downloading tomtom sat nav which I believe is around £50 to buy. It's the same with Android, except you 'root' your smartphone and that's more complicated to do with bigger risks.
Now Piratebay is not available in the UK because of a court ruling, there will be a lot of disappointed people out there who will have to start paying.