1. It is impossible to brick an iPad by jailbreaking it. A DFU-mode restore completely bypasses everything on the internal flash storage. Any software-induced system failure can be rectified.
2. Under UK consumer law Apple would have to prove that jailbreaking the device directly contributed to the reason for warranty claim.
3. Jailbreaking != piracy. Some choose to use it as a mechanism by which to facilitate it, but personally I use it to install the standard suite of Unix tools for work purposes. These tools are free and open source, hence you cannot "pirate" them. The pirates are usually children who can't afford them and hence would not buy them anyway, or adults who could afford them but would never pay because they're tight (I know plenty of these). Whilst I don't for 1 minute condone software piracy the same is true in that as it is of music; the vast majority of pirated copies do NOT represent a lost sale, a fact which content providers repeatedly ignore because it does not suit their extortion strategy.