“SDK” is a much less useful hard boundary than “Web API” for where I stop providing service. Should I provide an SDK in every language a client might use? If they want to access my service in a language I don’t support, should I tell them to piss off? I could offer for them to just hit the API themselves, but then we’re back where we started.

On the other hand, if I offer a web service and some someone asks “but what if I can’t make HTTP requests?” I’m _perfectly_ happy to tell them to piss off.