I'd define the "general purposeness" by the public availability of an official SDK. Video game consoles are strange because there's no agreement whether they are appliances or not. Most of them also have unofficial public SDKs. Heck, some people would even say that routers are general purpose computing devices and install a custom OS on theirs.
Apple's SDKs are "public" in the sense that you can go read them, but if you want to ship anything with them on iOS, you need a paid developer account, right? I wouldn't call that public.
