A POV of "repeatability" which is missed: It's not so much that you're buying a repeatable $4 item, it's that you're paying thousands of dollars for something instantiated over and over. You're not so much buying the individual drink as buying into Starbucks. You've made your evaluation, considered the options, and settled on a product for which you are going to shell out a pile of cash, using it for a long time (in $4 20oz increments). This vs. apps which, as you note, requires evaluation every time with a different experience for each $1. The "coffee vs. app" comparison would only be valid if every time you bought a drink you weren't quite sure what you were getting, knowing that there was high odds of chucking it on the first sip; you wouldn't be buying many of those either. The coffee analogy matches more the device you're running the app on: same device, used in small increments daily, with a little surface variation (the apps), for a very long time; this matching more that you're buying the Starbucks experience for $2 a day, and swapping out toppings/flavorings (apps) for another $1 or so.

BTW: the correct order is "short black". "Tall" isn't their smallest size, the un-advertised "short" is. They may not have the proper cups (as most customers don't know they exist), so you may get a free upgrade to "tall". As for "black", why would anyone want to adulterate a perfectly good coffee into a milkshake?