"but we will always have at least the original black box's capabilities."
Are you sure? I'm not. And replacing them may still be complex.
You may found the service you were using didn't generate enough revenues, so it gets shutdown, and an alternative may not be available. They may increase prices beyond what you are willingly to pay, maybe including a lot of orchids and mushrooms support you're not interested in at all, changing their interfaces in ways that force you to rewrite your script from scratch. Or maybe they'll drop roses support because the new fashion are tulips.
If we are speaking about simple services, it's probably they'll exist for a long enough time. The issue will be more specialized services. I've seen interesting products disappear when bought by someone who saw advantages in using them exclusively, because of the competitive edge.