I just like to know why things work and are done the way they are done, so in winpwn "Why do i have to pwn iTunes"? Can i just go to a brand new iTunes install on a new PC and do a restore via "shift + click" and select a custom firmware?

Or does pwning iTunes allow you to Shift+click ?
or does pwning iTunes allow the cusom firmware to have a valid checksum?

Can someone tell me why? I see a lot of "you have to do it this way" but i like to know why.