"many (not all) people jailbreak for access to pirated apps" -- on what do you base that conclusion. It's not like the Cydia store offers pirated apps. I think most people jailbreak their iPhones to get useful apps that Apple will not approve for the Apple store. In most cases Apple doesn't approve these apps because they compete with an Apple product or take away from the gouging...er...I mean revenue desires of Apple or AT&T Wireless.
Two examples of this which apply to why I jailbreak my iPhone: Google Voice and data tethering. Apple wouldn't approve the Google Voice for the Apple Store. Apple/ATTWS only started offering data tethering with iOS 4.0...and you have to pay ATTWS an extra $20 a month (charing you a monthly fee to use data you're already paying for). Not only that, you have to get rid of your unlimited data plan and get a tiered data plan.
A jailbroken iPhone has allowed me to tether my iPhone and/or use it for a mobile hot spot using my current iPhone's unlimited plan w/o having to pay ATTWS an extra $240/year for the privilege of using my own data.