Can't say I've ever noticed any music in Pret... nor do they have existing wifi hotspots. Starbucks on the other hand actually try to sell music in their stores already so there's at least some kind of synergy...
I love Pret a Manger, and I'd also love them to hook-up with Apple. But I doubt this would happen simply because they're not as widespread as Starbucks. I think Apple will probably follow the model they've proposed/are adopting in the US, then maybe other chains/retailers/cafés will become interested... Let's see