Huh? I have tons of apps that use Passbook? I use Passbook daily for rewards cards and loyalty cards? Here is a link to a huge list of apps integrated into Passbook: http://en.wikipedia.org/wiki/Passbook_(application)
I have personally used it tons of times with my Starbucks card, Walgreens card, and for tickets to get into concerts.
For example, when flying to Germany I had the Lufthansa app. An hour before the flight it popped up on my home screen and stuck there. (As in, no cancel.)
Then when I go to the airport, I swiped it and the lady just scanned it in - and me and my girlfriend both had our tickets printed.
In most (almost all?) cases the cashier can manually enter the number on the front of the card in to their register. For example, if the magnetic stripe on the back of the card was wearing out or damaged.