Jailbreaking is not the same as piracy. Jailbreaking is legal allows you to use your iPad in ways Apple do not intend and install whatever apps you like, provided you do not infringe Apples copyrights. The JB apps do not have to be approved by Apple and sold through the App store. But that freedom is NOT an excuse to steal software which is normally paid for. THAT is piracy and strictly ILLEGAL.
Jailbreaking has no equivalent on a PC because you are not restricted to only install software from one controlled source. However, just like a PC, if you pirate software which should normally be paid for, that is illegal too.