You still need to install the apps to have them appear in passbook anyway.
The question is if its any quicker to get to them. In pure tapping its not you need to go into passbook and find the relevant tab. Two taps. In many cases two taps gets you to the scannable area in the actual app, and offers additional functionality if you need it, like seeing that you dont actually have enough cash in your Starbucks card and being able to top it up. If you realise that in Passbook its a home button tap and another two presses.
You have to have an awful lot of such apps and a problem finding them on your homescreens before this becomes a genuine issue. As far as I can see the only benefit for developers is that if you play ball Apple might put you in the featured section of the App Store, which is a massive driver of app installations.
What might have made passbook better was if there was a standardised way to create files for scannable tickets that could be emailed as an attachment, like iCal appointments. I get emailed loads of tickets that an app that pulled them together and presented them in date order to be scanned would be helpful if companies bought into it rather than having to hunt for the mail from three months ago when I bought the ticket. But Im not going to install a bunch of providers apps to do this, I might never use these people again and its crazy clutter.