There's already social anxiety when people pay for things and walk past a security guard, or a security barrier. Whether it's an airport, or a clothes store, or a ticket barrier, there's always a nervousness about being called out.
It's bad enough in the Apple Store where you can pay and walk out, this will take some real getting used to.
I've used the Apple Store feature to buy a charger and iPhone case in the past. I admit it did feel strange as I waltzed out the front door past the genius bar guys just holding an item in my hands. If I had a bag I could put the item into (I imagine I could've asked a worker for one) then I would probably just look like every customer who paid at the till.
This leads me to think that the reason I felt weird is because I was the only one walking out of the store (to my knowledge) that paid in this manner. If I know everyone is doing it, again my mind would probably be at ease.