Coffee shop CRM

I went to Pret today on Charing Cross Road to get lunch. They'd run out of brie baguettes, so they gave me a free coffee while somebody ran downstairs and made one.
Now unfortunately, I don't like Pret coffee very much. I think I'm used to Cafe Nero too much (twice as much espresso per cup, and thus a proper taste, whereas Pret tastes more like warm coffee flavoured milk).
But not to look a gift horse in the mouth, several ideas suggest themselves:

• Pret are so keen to keep customers loyal that they'll give away a cup of coffee every time they fail to live up to expectations


• Pret make so big a profit on every sandwich that they can afford to give away coffee


• Somebody, somewhere at Pret has a spreadsheet and they've worked out the lifetime value of a customer is better if occasional sandwich-provision-failure is compensated for by free coffee, because the long term value maximises their return

But I'm not sure about the value of customer loyalty. After all, this is a busy thoroughfare, frequented by all sorts of passing trade. Just because I have a good experience in Pret once doesn't necessarily imply I'll ever be back.
On the other hand, maybe I'll now feel that Pret in general is so generous that I'll favour them over other coffee shops in future. So although they've lost out in the short term, long term loyalty improves.
Perhaps it's a different situation in central London to elsewhere. After all, on the way to Pret I've got Eat, Subway, a coffee shop whose name I can't remember, and that's before I've even left Soho Square. Then there's Benjy's, the competing Italian place over the road, Starbucks ... if it wasn't for this density of coffee shops, perhaps loyalty would be more important. Or less important: if there was only Pret and nobody else on the street, they'd hardly need to work to keep me loyal.
All that said, it wasn't a great sandwich, and even a free cup of Pret latte isn't as good as a paid-for Cafe Nero one. So have I learnt anything from this?